The effect of gestation and of protein quality on the nutritive utilization of protein

A study was made of the effect of protein quality on gestation and on digestive and metabolic utilization in Wistar rats. The protein level of the diet was 14%, and the protein sources used were: casein, beans and a mix of beans and wheat, in order to complement the essential amino-acids deficient in both protein sources. Gestation increased food intake in the 3 groups of experiments, in which distinct protein sources were used. Protein quality did not affect food intake in the two physiological situations under study (gestation and non-gestation). In pregnant animals, the greatest weight gains were obtained with the casein diet, while in non-pregnant ones the weight increases were greater with the diet of beans and wheat. The smallest gains recorded were those of pregnant and non-pregnant rats fed a diet of beans. Gestation did not affect protein-absorption. The digestive utilization of protein was superior with the casein diet. The study of nitrogen retention showed: 1. The pregnant animals retained more nitrogen than the non-pregnant animals with all of the diets under study. 2. In pregnant animals, the greatest metabolic utilization took place with the casein diet, with little difference between the bean and bean-wheat mix diets, although in the latter it was slightly superior.     

Progesterone concentration in the marsupial Sminthopsis macroura: relationship with the conceptus, uterine glandular regeneration and body weight

Close examination of hormonal profiles and uterine morphology in the marsupial reproductive cycle highlights significant differences between pregnant and non-pregnant cycles. In the polyovular dasyurid marsupial Sminthopsis macroura, we identified changes associated with gestation by comparing ovarian and plasma progesterone concentrations, uterine weights, uterine epithelial mitoses, body weights and gestation lengths between pregnant and non-pregnant luteal phases. The plasma progesterone profile of S. macroura was biphasic, peaking during unilaminar blastocyst expansion and on the day of implantation. Periods of rapid embryonic development were associated with increasing plasma progesterone concentrations and animal body weight. For the first time in a polyovular marsupial, we identified 1) a correlation between ovarian progesterone concentration and conceptus number during the luteal phase just prior to implantation (total ovarian progesterone), indicating a conceptus influence on progesterone concentration; 2) a pulse of uterine epithelial mitotic activity at the time of implantation and 3) increased mitotic activity in pregnant animals during unilaminar blastocyst formation compared with non-pregnant animals. Gestation length was reduced by up to 15%, due to the loss of, or reduction in, the four-cell arrest and more rapid definitive blastocyst expansion. This is the first time a conceptus influence on gestation length has been identified in a dasyurid. This study provides further evidence for the modification of the luteal phase by pregnancy in S. macroura.     

Influence of gestation and hydrocortisone-acetate treatment on the nutritive utilization of protein

The effect of pregnancy and of cortisol on the digestive and metabolic utilization of protein in Wistar rats was studied. The cortisol is i.m. administered during 21 days in a pharmacological dose (4 mg/100 g weight per day) to female Wistar rats. Pregnancy is observed to increase and cortisol to decrease significantly the food intake (g dry matter/rat per day); the intake of nitrogen follows the same pattern. Pregnancy significantly increases the weight of both groups: pregnant rats as comparison to non-pregnant rats saline injected and pregnant rats cortisol-treated in relation to the animals pregnant but not hormone-treated. The increase being greater in the last 5 days of pregnancy. Cortisol in the pregnant and non pregnant rats considerably reduces the weight. The protein absorption is unaltered by pregnancy but is diminished by the effect of cortisol. Pregnancy increases the balance of nitrogen in both sets of rats; the increase being significantly greater in the last period of pregnancy. When administered to non pregnant rats, cortisol produces a negative balance of nitrogen. The protein of good quality (casein + 5% DL-methionine at a level of 12%) partially equalizes the negative effect of cortisol in spite of the long treatment and high doses used.     

酿造鲜味酱油调节大鼠血压机制的研究

将雄性SD大鼠随机分成普通饮食（ND）组、高脂和高盐饮食（HFHS）组、高脂和酱油饮食（HFSS）组,连续灌胃10周,测定基础代谢参数及影响血管紧张素及醛固酮分泌的相关生物参数,考察鲜味酿造酱油（盐含量8%）通过肾素-血管紧张素-醛固酮系统（RAAS）调节大鼠血压的机制。结果表明,各组SD大鼠食物摄入量无显著差异（P＞0.05）。与HFHS组相比,HFSS组SD大鼠水摄入量无显著差异（P＞0.05）,体质量、血压显著下降（P＜0.05）,但尿液排出量显著增加（P＜0.05）;血清中总胆固醇、甘油三酯、血管紧张素Ⅱ和醛固酮含量显著下降（P＜0.05）,尿液中的钾离子显著增加（P＜0.05）;肾脏中血管紧张素1型受体、类固醇11β-羟化酶及醛固酮合成酶基因的表达水平显著下降（P＜0.05）,钠钾腺嘌呤核苷三磷酸（ATP）酶α1基因的表达水平显著增加（P＜0.05）,说明酿造鲜味酱油可通过RAAS调节血压。     

Influence of hydrocortisone acetate of the longissimus dorsi muscle during gestation of rats

The evolution in detail of the N retention during gestation was studied, dividing it in short periods of time, and how that retention affects Longissimus dorsi muscle. Simultaneously, the same study in pregnant rats treated with hydrocortisone acetate was done. During gestation N balance maintains high values that tend to increase at days 18 to 21. The greatest metabolic utilization of the N dietary corresponds to this period in which the percentage of the N retained in relation to the N absorbed is markedly higher than in previous days of gestation. In spite of the excellent quality and adequate concentration of protein in the diet, the administration of 4 mg/100 g weight and day of hydrocortisone acetate maintains the pregnant rat in a negative balance until day 18, as a consequence of the decrease in food intake and faecal and urinary N losses. From day 18 to day 21 of gestation the balance of N increases and the metabolic utilization of the dietary N is similar between pregnant rats injected with NaCl 0.9% and pregnant rats injected with hydrocortisone acetate. The Longissimus dorsi normal growth pattern (in relation to weight and N content) in young adult rats is not modified by gestation. The catabolic effects of hydrocortisone acetate on Longissimus dorsi muscle in pregnant rats can be observed from day 9 of treatment. The longer the treatment the higher the effect is.     

The effects of a high-fat, high-cholesterol diet on markers of uterine contractility during parturition in the rat

Increasing levels of obesity within women of reproductive age is a major concern in the UK. Approximately, 13% of women aged <30 and 22% of 31- to 40-year-old women are obese. Obesity increases complications during pregnancy and the risk of caesarean section due to prolonged labour and poor uterine activity. The aim was to investigate whether a high-fat, high-cholesterol (HFHC) diet decreases markers of uterine contractility during parturition in the rat. Female Wistar rats were fed control (CON, n=10) or HFHC (n=10) diets for 6 weeks. Animals were mated and, once pregnant, maintained on their diet throughout gestation. On gestational day 19, rats were monitored continuously and killed at the onset of parturition. Body and fat depot weights were recorded. Myometrial tissue was analysed for cholesterol (CHOL), triglycerides (TAG), and expression of the contractile associated proteins gap junction protein alpha 1 (GJA1; also known as connexin-43, CX-43), prostaglandin-endoperoxide synthase 2 (PTGS2; also known as cyclo-oxygenase-2, COX-2) and caveolin-1 (CAV1) and maternal plasma for prostaglandin F(2)(α) (PGF(2)(α)) and progesterone. HFHC fed rats gained greater weight than CON (P<0.003) with significant increases in peri-renal fat (P<0.01). The HFHC diet increased plasma CHOL, TAG and progesterone, but decreased PGF(2)(α) versus CON (P<0.01, P<0.01, P=0.05 and P<0.02 respectively). Total CHOL and TAG levels of uterine tissue were similar. However, HFHC fed rats showed significant increases in PTGS2 (P<0.037), but decreases in GJA1 and CAV1 (P=0.059). In conclusion, a HFHC diet significantly increases body weight and alters lipid profiles that correlate with decreases in key markers of uterine contractility. Further work is required to ascertain whether these changes have adverse effects on uterine activity.     

Influence of dietary protein on performance of dairy goats during pregnancy.

An experiment was conducted utilizing 44 Alpine does (48 kg of BW) to examine the effects of dietary protein intake on nutritional status and performance of does during the latter half of pregnancy and parturition. All dry does were bred, confirmed pregnant, and fed a diet containing 9% CP and 2.04 Mcal of metabolizable energy/kg of DM through wk 11 of gestation. On wk 12, does were blocked by BW and assigned to one of three dietary treatments: 8.8% (low) CP, 11.0% (medium) CP, and 14.3% (high) CP. All diets were isocaloric (2.04 Mcal of metabolizable energy/kg of DM) and fed for ad libitum intake from wk 12 of gestation until parturition. Average CP intakes for low, medium, and high protein were 164, 220, and 303 g/d, respectively. Body weight gains increased with increasing CP intake. Kidding rates were 79, 100, and 93% for the low, medium, and high protein groups. Gestation length, litter size, and litter weight did not differ among treatment groups. Urea N in jugular blood plasma increased with increasing CP intake. Plasma glucose and whole blood beta-hydroxybutyrate tended to increase with increasing CP intake. Plasma glucose decreased 7, 6, and 3%, and NEFA increased 97, 400, and 187% between wk 13 and 21 of gestation for the low, medium, and high protein diets, respectively. The data suggest that the low protein diet may be inadequate to meet the does' protein requirement during late gestation, but there was no apparent advantage in feeding the high rather than medium protein diet. Intake of CP for the medium protein diet, 9.8% g/kg of BW.75, was 40% higher than that recommended by the NRC for pregnant goats.     

Effects of sodium bicarbonate or sodium sesquicarbonate on lactating Holsteins fed a high grain diet

Fifteen Holstein cows, 35 to 70 d postpartum, were assigned to five 3 x 3 Latin squares. Treatments were: control (60% concentrate, 40% corn silage, DM basis) or control supplemented with either .71% sodium bicarbonate or .65% sodium sesquicarbonate, DM basis. Orthogonal contrasts compared the effect of both buffered diets versus the control diet, and the effect of sodium bicarbonate supplementation vs. sodium sesquicarbonate supplementation. There were no differences among treatments for milk yield (34.9 kg/d), milk fat yield (.99 kg/d), 3.5% FCM (31.1 kg/d), or milk protein concentration (3.15%). There were no treatment effects on total chewing time. Milk fat concentration tended to be greater for cows fed sodium bicarbonate (2.92%) and sodium sesquicarbonate (2.89%) relative to control (2.82%). Relative to control, sodium bicarbonate and sodium sesquicarbonate supplementation increased DM intake (22.0 and 22.7 vs. 21.4 kg/d), digestible DM intake (16.7 and 16.2 vs. 14.8 kg/d), digestible organic matter intake (16.0 and 15.5 vs. 14.3 kg/d); and apparent digestibility of DM (77.3 and 74.8 vs. 73.3%) and NDF (62.6 and 56.5 vs. 54.7%). Relative to sesquicarbonate, bicarbonate supplementation increased apparent digestibilities of CP (82.3 vs. 78.8%) and NDF, and decreased milk protein yield (1.06 vs. 1.11 kg/d). Sesquicarbonate was as effective as bicarbonate in alleviating milk fat depression and increasing intake of digestible organic matter.     

低钠复合盐对发酵香肠理化特性及风味的影响

以添加58%氯化钠、30%氯化钾、7%氯化钙、5%甘氨酸的低钠复合盐发酵香肠作为实验组,以100%氯化钠为对照组,通过测定理化指标、感官评价、电子舌味觉特征、游离氨基酸含量以及挥发性风味物质等探究低钠复合盐对发酵香肠品质的影响。结果表明：在香肠发酵成熟过程中,香肠pH值、水分含量呈显著下降趋势,钠含量显著增加。实验组pH值显著低于对照组,水分含量显著高于对照组,并且对产品的色泽和质构特性有一定改善作用,实验组在显著降低钠含量的同时,感官评价与对照组无明显差异。根据电子舌分析,实验组的鲜味、丰富度、苦味显著高于对照组。此外,实验组促进了游离氨基酸的释放,并对挥发性风味物质的产生没有负面影响。因此,实验组在减少42%食盐添加量的基础上,保证了发酵香肠良好感官和风味品质。     

The effect of oat hulls,added to the basal ration for pregnant sows,on reproductive performance,apparent digestibility,rate of passage and plasma parameters

Thirty-five Large White x Landrace sows were housed in individual stalls during gestation and were fed a standard diet (DE, 13.2 MJ kg^?1) supplemented with oat hulls (OH), such that the ratios of basal diet to OH were 1:0, 9:1, 7:3 or 1:1. Digestibility and balance measurements were made during 7-day periods beginning on days 45 and 90 of gestation. During a 3-week lactation all sows were fed a standard diet (calculated DE, 12.5 MJ kg^?1, CP, 152 g kg^?1). Increasing OH intake increased mean net maternal weight gains and P2 fat depths during pregnancy and tended to increase total litter weight at birth. Sow-milk solids content and litter weight gain during the 3-week suckling period also tended to increase (nonsignificant), following increasing OH supplementation during gestation. Increasing OH intake tended to increase VFA and reduce cholesterol concentration in blood plasma at 56 days of gestation. The time taken to consume the once-daily feed allowance increased and gastrointestinal transit time decreased as OH intake increased. The apparent digestibilities of the major nutrients were significantly depressed with increasing levels of OH in the diet but the total amounts of nutrients absorbed increased. The following values were calculated for OH by the difference method: apparent digestibility of DM, 0.31; apparent digestibility of ADF, 0.17; DE, 6.25 MJ kg^?1; ME 6.01 MJ kg^?1.     

大鼠繁殖试验评价牛初乳对生殖发育的影响

目的通过繁殖试验观察牛初乳对亲代大鼠生殖及F1代仔鼠发育状况的影响,评价牛初乳的生殖发育安全性。方法选用4周龄SD大鼠,牛初乳组在交配前期、宫内暴露期、哺乳期和仔鼠性成熟期(受孕前11周至仔鼠性成熟),用含10%牛初乳的饲料喂饲亲代和子代大鼠,对照组饲喂普通饲料,检测亲代体重、摄食量、动情周期、繁殖力指数、怀孕指数、孕周、每窝活产数、激素水平、生殖器官及精子质量;子代出生体重及身长、性别比、4日生存率、阴道开口时间、包皮分离时间等。采用两独立样本t检验的统计方法对均数进行比较,使用SPSS 13.0统计分析软件处理数据。结果与对照组相比,牛初乳对亲代的动情周期、繁殖力指数、怀孕指数、孕周、每窝活产数、子代性别比、出生身长、4日生存率均无显著影响,但亲代雄鼠左侧储精囊脏体比降低,精子总数提高(P<0.05),且牛初乳组亲代雌、雄大鼠血液中的促黄体生成素(LH)显著降低(P<0.05),雌鼠血液中催乳素(PRL)和孕酮(P)均显著低于对照组(P<0.05)。结论一代繁殖试验未发现牛初乳对生殖发育能力有显著影响,仅见亲代储精囊、精子总数和激素水平改变,其长远影响需二代繁殖试验进一步验证。     

8-HYDROXY-2'DEOXYGUANOSINE LEVELS AND ANTIOXIDANT STATUS IN RAT LIVER FED WITH OLIVE AND CORN OIL DIETS: EFFECT OF ASCORBIC ACID SUPPLEMENATION

DNA damage and antioxidants status were determined in liver of rat fed with olive and corn oil diets with and without ascorbic acid supplementation. In order to elucidate the role of fat intake, the study included a control and hyperlipidic diet. Liver antioxidant activities were significantly influenced by dietary fat and intake levels. In general, control groups fed with corn oil diets exhibited reduced liver antioxidant (SOD, catalase, and GSH-PX) and GSH levels compared with rats fed on olive oil diets. These activities were lower in rats consuming hyperlipidic diets relative to the control groups. Ascorbic acid supplementation resulted in a slight decrease of antioxidant activities both in the control and hyperlipidic diets with the exception of GSH that showed high levels in rats fed on an olive oil diet supplemented with ascorbic acid. The results of oxidative DNA damage as measured by the induction of 8-hydroxy deoxyguanosine (8-OHdG) clearly confirmed that corn diet (rich in polyunsaturated fatty acids) induced DNA damage in a dose- dependent manner. No induction of 8-OHdG was detected for the diet containing olive oil (monounsaturated diet). Ascorbic acid had no effect on rat fed on an olive oil diet. In contrast, for corn diets the ascorbic acid showed     

低钠盐对不同成熟条件下自然发酵牦牛肉灌肠脂质氧化及挥发性风味物质的影响

探究降低钠盐含量对自然发酵牦牛肉灌肠脂质氧化及风味品质的影响。分别添加2%（低钠盐）和4%（对照）钠盐制备灌肠,并分别以自然成熟和恒温成熟两种方式制备成品,测定成熟过程中相关理化指标。结果表明,两种成熟方式中低钠盐组的水分含量、1,1-二苯基-2-三硝基苯肼自由基清除能力和羟自由基清除能力均显著低于对照组（P＜0.05）,而pH值显著高于对照组（P＜0.05）。4 种处理组灌肠脂质水解和脂质氧化程度随时间延长升高,成熟过程中两种成熟方式中低钠盐组的脂质水解、氧化程度均显著高于对照组（P＜0.05）;自然成熟的两组灌肠脂氧合酶活力无显著差异（P＞0.05）,而后期恒温成熟灌肠低钠盐组脂氧合酶活性显著高于对照组（P＜0.05）。此外,从灌肠中共检出69 种挥发性风味物质,3 个主成分累计贡献率达96.206%。主成分分析结果表明,第9天和第17天成熟结束,低钠盐组中由脂质氧化生成的醇、醛等物质的相对含量较对照组多。不同钠盐含量对灌肠的脂质水解、氧化有显著影响,直接减少钠盐质量分数至2%,可能会促进脂质的氧化。     

Effects of diet supplementation with cactus pear seeds and oil on serum and liver lipid parameters in rats

The purpose of this investigation was to evaluate the effects of diets enriched with cactus pear oil (CPO) or seeds (CPS) on serum and liver lipid parameters compared to those of adult rats submitted to a standard diet. Male rats were divided into three groups, the first group represented control group, fed with standard diet, the second group was fed with control diet supplemented with CPO (2.5%, wt/wt) and the third group fed control diet supplemented with CPS (33%, wt/wt), for nine weeks. Feed intake and body weight of rats were measured every two days. Organ weights were determined at the end of treatment; cholesterol, HDL and triglycerides levels were determined by enzymatic methods. Liver and serum lipid extracts were analysed for their fatty acid composition for the three groups of rats. No differences in pancreas, kidney or liver weights were observed in the CPS diet whereas the CPO diet induced a significant increase in liver and pancreas weights. The tested diets significantly decreased the atherogenic index compared to the control diet, whereas serum cholesterol level was only reduced by the supplementation with CPO diet. No variations in serum lipids were observed among the groups, whereas liver lipids showed slight variations. Accordingly, these results indicated that the supplementation with CPO or CPS could be effective in decreasing the atherogenic risk factors in rats.     

孕妇妊娠期糖尿病调查及其与饮食状况的关系分析

目的探讨孕妇妊娠期糖尿病调查及其与饮食状况的关系分析。方法回顾性调查2014年9月至2017年9月本院收治552例孕妇的临床资料,分析孕妇饮食状况与妊娠期糖尿病的关系。结果本次调查中,妊娠期糖尿病孕妇54例(9.78%);妊娠期糖尿病孕妇和健康孕妇日摄入总能量、年龄、孕次水平基本相同,差异无统计学意义(P0.05),妊娠期糖尿病孕妇孕前BMI、脂肪摄入量、蛋白质摄入量、碳水化合物摄入量和甜食喜好、夜宵食用、荤菜量过多、豆制品量过少占比明显高于健康孕妇,差异有统计学意义(P0.05);logistic回归分析法显示,脂肪摄入量、甜食喜好、荤菜量过多、豆制品量过少是孕妇妊娠期糖尿病发生的危险因素(P0.05)。结论孕妇的饮食状况与妊娠期糖尿病的发生有关,应重视脂肪摄入量、甜食喜好、荤菜量过多、豆制品量过少等孕妇的营养干预,以防治娠糖尿病的发生。     

Suppression of leptin-induced hypothalamic JAK/STAT signalling and feeding response during pregnancy in the mouse

Hyperphagia during pregnancy, despite rising concentrations of the satiety hormone leptin, suggests that a state of leptin resistance develops. This study investigated the satiety response and hypothalamic responses to leptin during pregnancy in the mouse. Pregnant (day 13) and nonpregnant mice received an i.p. injection of either leptin or vehicle and then 24-h food intake was measured. Further groups of pregnant and nonpregnant mice were perfused 2 h after leptin or vehicle injections and brains were processed for pSTAT3 and pSTAT5 immunohistochemistry. Leptin treatment significantly decreased food intake in nonpregnant mice. In pregnant mice, however, leptin treatment did not suppress food intake, indicating a state of leptin resistance. In the arcuate nucleus, leptin treatment increased the number of cells positive for pSTAT3, a marker of leptin activity, to a similar degree in both nonpregnant and pregnant mice. In the ventromedial nucleus (VMN), the leptin-induced increase in pSTAT3-positive cell number was significantly reduced in pregnant mice compared to that in nonpregnant mice. In nonpregnant mice, leptin treatment had no effect on the number of pSTAT5-positive cells, suggesting that in this animal model, leptin does not act through STAT5. In pregnant mice, basal levels of pSTAT5 were higher than in nonpregnant mice, and leptin treatment led to a decrease in the number of pSTAT5-positive cells in the hypothalamus. Overall, these results demonstrate that during pregnancy in the mouse, a state of leptin resistance develops, and this is associated with a reduced sensitivity of the VMN to leptin.     

肉制品绿色制造——低钠干腌肉制品研究进展

干腌肉制品因其具有独特的色泽、风味和口感等感官特性而深受广大消费者的喜爱。然而传统干腌肉制品的钠盐（氯化钠）含量过高,人体摄入过高的钠盐会对健康产生不良影响。本文讨论了食盐对干腌肉制品风味、质构和微生物安全的影响,概述了低钠干腌肉制品的相关研究动态,并对低钠干腌肉制品绿色制造的未来研究（如低钠复合盐）提出展望。     

低盐对发酵肉制品品质形成影响及减盐手段研究进展

食盐是发酵肉制品加工过程中不可或缺的腌制材料,具有提供咸味、抑菌、提高加工及品质特性等作用。为了抑制发酵过程中致病菌和腐败菌生长,保证产品安全性,发酵肉制品常需高含量盐分。但摄入过多的食盐会对人体健康产生负面影响,因此,降低发酵肉制品中食盐的添加量势在必行。本文简单介绍了食盐在发酵肉制品中的作用及其对微生物的影响,论述了低盐处理对肌肉蛋白和脂质水解、氧化作用以及品质形成的影响,最后综述了常用的减盐手段,以期为发酵肉制品减盐研究提供理论依据。     

Effects of in vivo administration of epidermal growth factor (EGF) on uterine contractility, prostaglandin production and timing of parturition in rats

Prostaglandins synthesized by cyclooxygenases elicit uterine contractions during labour. Nitric oxide synthases (NOS) produce nitric oxide (NO), which maintains uterine quiescence during pregnancy. Epidermal growth factor (EGF) interacts with prostaglandins and NO in many biological systems. The aim of this work was to study the effect of the in vivo administration of EGF on uterine contractility, prostaglandin production and timing of parturition in rats. EGF was injected into the uterine lumen of pregnant rats on day 20, 21 or 22 of gestation. Intra-uterine administration of 500 ng EGF on day 21 of gestation delayed parturition for 18 h compared with control rats. Administration of EGF was able to: (i) reduce cyclooxygenase expression in the uterus (determined by western blot analysis) and production of prostaglandins by the uterus (evaluated by conversion of [(14)C]arachidonate to labelled prostaglandins); (ii) decrease prostaglandin concentrations in amniotic fluid (radioimmunoassay); (iii) increase NO production (evaluated by conversion of [(14)C]arginine into [(14)C]citrulline); (iv) increase serum progesterone concentrations to more than control concentrations (P<0.05; radioimmunoassay); and (v) reduce the amplitude of the uterine contractions. The overall effect was a delay in the onset of delivery. This in vivo effect raises the question of whether exogenous EGF plays a role in the initiation of parturition.     

Expression of small heat shock-related protein 20 (HSP20) in rat myometrium is markedly decreased during late pregnancy and labour

The underlying mechanisms regulating uterine contractions during labour are still poorly understood. Heat shock protein 20 (HSP20) is known to be present at high levels in smooth muscle and implicated in muscle relaxation, but HSP20 expression in the myometrium is completely undetermined. Since HSP20 has been implicated in smooth muscle relaxation, we hypothesized that HSP20 would be highly expressed in the rat myometrium during early and mid-pregnancy when the myometrium is relatively quiescent. Northern blot analysis particularly demonstrated that HSP20 mRNA detection was significantly decreased from day (d) 22 of pregnancy to 1-day post-partum (PP) compared with d6 (P < 0.05). HSP20 mRNA detection was also significantly decreased from d22 to d23 of gestation compared with non-pregnant (NP) samples. Immunoblot analysis showed that detection of HSP20 was significantly decreased at d23 compared with d12 and d15 (P < 0.05). HSP20 detection also significantly decreased at PP compared with d15 (P < 0.05). Immunofluorescence analysis demonstrated that after d15, plasma membrane-associated localization of HSP20 decreased markedly in both circular and longitudinal muscle layers. In addition, HSP20 was detectable near cell membranes at much higher levels in the longitudinal muscle layer of progesterone-treated pregnant rats (delayed labour) at all gestational time points examined, compared with controls. Our results demonstrate that HSP20 mRNA and protein are highly expressed during early and mid-pregnancy and then the expression markedly decreases during late pregnancy and labour. The observed patterns of HSP20 expression are consistent with a potential role for HSP20 in facilitating myometrium quiescence during early and mid-pregnancy.