Pituitary control of growth in the neonatal rat: effects of neonatal hypophysectomy on somatic and organ growth, serum insulin-like growth factors (IGF)-I and -II levels, and expression of IGF binding proteins.

The neonatal period is a time of transition between pituitary-independent fetal growth and the pituitary-dependent growth seen in older mammals. To evaluate pituitary-dependent neonatal growth, Wistar rats were hypophysectomized (Hx) on postnatal day 6. Nineteen days post-Hx, body weight and tail length were inhibited 48% and 34%, respectively, compared with sham-Hx controls. Organ weights determined on days 10, 15, 20, 25, and 30 revealed three patterns of pituitary-dependence: 1) pituitary-independent growth in the brain and lung; 2) moderate pituitary-dependent growth in the heart, liver, kidney, and intestine; and 3) marked pituitary-dependent growth in the adrenals, spleen, and testes. Both serum insulin-like growth factor (IGF)-I and -II levels fell significantly in Hx pups by 54 h after Hx (P = 0.0005), and Northern analysis on day 15 showed a significant decrease in liver messenger RNA (mRNA) for IGF-II. Analysis of the major IGF binding proteins (BPs) was performed by Western ligand blots. Hx performed on day 6 resulted in a linear decrease in the amount of the 22k BP from day 10 to day 30. In contrast, the major neonatal BP (IGFBP-2, a 29.5k molecule) showed a biphasic response to neonatal Hx. On postnatal day 10, 4 days after Hx, a significant decrease in IGFBP-2 occurred, which persisted through day 15; by postnatal day 20 and continuing through postnatal day 30, the amount of IGFBP-2 in the serum dramatically increased. The 40 to 50k fraction of IGFBP-3 first appeared in significant quantities by postnatal day 20, and after Hx dropped to 10% of sham-control values. Similarly, Northern analysis on day 15 demonstrated a significant decrease in liver, but not brain, mRNA for IGFBP-2 after Hx, whereas on postnatal day 25, liver mRNA for IGFBP-2 was increased in Hx pups compared with sham controls. We conclude that the pituitary gland exerts significant but selective effects on neonatal growth, with the notable exception of brain growth. Serum levels of both IGF-I and IGF-II, as well as their BPs, are pituitary dependent in the neonatal period. Pituitary-dependent neonatal growth thus appears to be mediated by IGF and modulated by IGF-binding proteins. On the other hand, that portion of the persistent growth in the neonatal Hx rat that is independent of the pituitary-IGF axis may be a good model for investigation of fetal growth.     

Ontogeny of pituitary regulation of growth in the developing rat: comparison of effects of hypophysectomy and hormone replacement on somatic and organ growth, serum insulin-like growth factor-I (IGF-I) and IGF-II levels, and IGF-binding protein levels in the neonatal and juvenile rat.

We investigated pituitary regulation of growth during two critical stages of development in the rat, using hypophysectomy (Hx) with replacement of GH and/or T4. In the neonatal period (Hx on day 6), body weight and tail length were inhibited by 60% and 50%, respectively, while these parameters were inhibited by 80% and 85% by Hx in the juvenile period (Hx on day 45). Administration of T4 alone significantly increased skeletal growth (tail length) in neonatal Hx rats, while T4 alone proved ineffective in promoting somatic growth in juvenile Hx rats. GH effects were greater on body weight than on tail length at both stages of development. Replacement of both GH and T4 restored somatic growth to normal values during both time periods. The brain was the sole organ whose growth appeared to be independent of the pituitary. Hx reduced serum insulin-like growth factor-I (IGF-I) and -II in both age groups, and GH alone restored IGF-I and -II levels to the control range. The major IGF-binding proteins (IGFBPs) were analyzed by Western ligand blots. The effect of Hx on the predominant IGFBP was greater in the juvenile rat. T4 replacement in the neonate and GH replacement in the juvenile rat restored IGFBPs to control levels. We conclude that somatic growth in the rat is less pituitary dependent in the neonatal period. There are also important age-specific differences in organ response to GH and T4. Serum IGFs and their binding proteins are pituitary dependent even in infancy, and GH is their primary regulator. The neonatal Hx rat is an important model for the study of the dynamic development of the pituitary-dependent growth.     

Activation of rat gastric mucosal adenylyl cyclase by secretory inhibitors.

Prostaglandin (PG) E1, E2, A1, and A2 stimulated rat gastric corpus mucosal membrane adenylyl cyclase activity. PGE1 (Kalpha congruent to 8 muM) affected the maximum velocity but not the affinity of the enzyme for ATP and maximum PGE1 activation was not affected by histamine H1 or H2 receptor antagonists. 5'-Guanylyl-diphosphoimide (Gpp(NH)p), but not GTP, stimulated both the basal and PGE1-stimulated adenylyl cyclase activities, although the percentage stimulation by maximal PGE was the same with or without Gpp(NH)p. NaF stimulation was also additive to that of PGE1. Secretin also stimulated gastric mucosal adenylyl cyclase activity (Kalpha congruent to 30 nM). Maximal secretin activation was not additive to that of PGE1, suggesting a coupling to the same adenylyl cyclase catalytic site. These studies suggest that mucosal membranes may contain beta-adrenergic receptors. The adenylyl cyclase activating agents used in this study, PGE1, secretin, and the catecholamines, are all known inhibitors of gastric acid secretion, suggesting a possible involvement of cyclic AMP in the inhibition of acid secretion in the rat stomach.     

Insulin-like growth factors (IGFs) reduce IGF-binding protein-4 (IGFBP-4) concentration and stimulate IGFBP-3 independently of IGF receptors in human fibroblasts and epidermal cells.

Recent studies have provided a consensus that insulin-like growth factor-I (IGF-I) stimulates IGF-binding protein-3 (IGFBP-3) in vivo and in vitro. While it also appears well established that IGFBP-1 is inversely related to insulin concentrations, evidence regarding regulation of other IGFBP is inconclusive. Using immunoprecipitation and Western ligand blot, we have characterized the IGFBPs released into conditioned medium (CM) by cells from the adult human fibroblast cell line N3652 and the human epidermal squamous cell carcinoma line SCL-1. N3652 cells expressed IGFBP-3, IGFBP-2, a 24-kilodalton (kDa) IGFBP presumed to be IGFBP-4, and IGFBPs at 30 and 28 kDa. SCL-1 expressed IGFBP-3 and a putative IGFBP-4, with intermediate bands at 34 and 30 kDa. As determined by ligand blot of CM from confluent cells 72 h after the addition of peptides to serum-free medium, IGF-I and IGF-II potently stimulated IGFBP-3 in both cell lines, but otherwise IGFBP regulation in the two cells diverged. In N3652 cells, IGFBP-3 concentrations in CM increased to 700% and 800% of basal levels in the presence of IGF-I and IGF-II (at 100 ng/ml; n = 5 experiments), respectively. IGFBP-3 was not affected by insulin up to 10 micrograms/ml. In contrast, IGFBP-4 levels were diminished 54% and 73% by 100 ng/ml IGF-I and IGF-II, respectively, with no response to insulin. In SCL-1 cells, IGF-I and IGF-II were virtually identical in stimulating a mean 200% increase in IGFBP-3 (n = 5 experiments). Insulin was less potent, but caused a significant stimulation of IGFBP-3 levels. IGF-I, IGF-II, and insulin all stimulated an approximately 50% increase in IGFBP-4 concentrations. To test the hypothesis that IGF-induced alterations in IGFBP-3 and IGFBP-4 concentrations were regulated via the type 1 IGF receptor, we attempted to block IGFBP changes with type 1 IGF receptor antibody alpha IR-3 and to induce IGFBP changes with an IGF-II analog, [Leu27]IGF-II, with little affinity for the type 1 receptor. alpha IR-3 failed to block either the IGF-induced rise in IGFBP-3 in each cell line or the decline in IGFBP-4 in N3652 CM. [Leu27]IGF-II was as potent as IGF-II or IGF-I in inducing changes in IGFBP-3 and IGFBP-4 concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)