Some effects of hypophysectomy on gastrointestinal function and structure

Gastrointestinal effects of growth hormone

GH receptor immunoreactivity is found throughout the gastrointestinal tract. GH has proliferative effects upon intestinal epithelium, and influences enteroendocrine cell secretion, calcium absorption, and intestinal amino acid and ion transport. The proliferative effects of GH may be reflected in the increased incidence of neoplastic colonic polyps in individuals with long-term GH excess reported by some investigators. GH also increases hepatic cytochrome P450 expression, potentially altering drug and steroid hormone metabolism. Current clinical research efforts include the use of exogenous GH as a stimulant of gut growth and adaptation in patients who have undergone massive intestinal resection. Exogenous GH is also being studied in animal models of critical illness where it appears to increase intestinal glutamine uptake, which may prevent deterioration of the intestinal mucosal barrier.

Effects of growth hormone on intestinal morphology of genetically dwarf rats

Three groups of Lewis rat were studied: dwarf rats, genetically deficient in growth hormone; rehabilitated dwarf rats treated with exogenous growth hormone (GH); and normal wild-type rats. The small intestine of each animal was removed and simple random transverse sections were taken from the proximal and distal regions. The profile areas of villi, crypt and muscle were estimated by point count analysis and combined with intestinal length measurements to obtain absolute volumes. Villus and primary mucosal surface areas were estimated from intersection counts and linear measurements were made of epithelial cell height. Distally, villous volume and surface area were reduced by 42% and 39%, respectively, in the dwarfs compared with controls. These features were significantly smaller (P < 0.01) in dwarfs distally than proximally. Crypt volume and epithelial cell height were decreased equally in both proximal and distal regions of the intestine of dwarf rats. Following GH administration both features increased, crypt volume overshooting control values. These results indicate that GH deficiency has a subtle effect on intestinal morphology and that the intestine is more sensitive distally than proximally. Reconstitution with GH is capable of reversing many of these changes.

Brain ACTH prevents stress gastric lesions in rats

This study evaluated the effect of ACTH and several ACTH fragments on the development of gastric glandular lesions induced by cold-restraint stress in rats. Intracerebroventricular administration of ACTH1-39 dose-dependently (0.1-10 micrograms) inhibited stress gastric lesion formation. Studies with smaller molecular weight forms of ACTH (in a dose equimolar to 10 micrograms of ACTH1-39) revealed that ACTH1-13 and ACTH1-10 were also protective. The ACTH fragments ACTH5-10, ACTH34-39 and ACTH1-17 were without effect. Immunoneutralization of endogenous brain ACTH1-39 significantly increased stress gastric lesion severity. Antisera raised against synthetic somatostatin, gonadotropin-releasing hormone, and L-enkephalin were ineffective. These results with ACTH coupled with our previous demonstration of a protective effect of beta-endorphin suggest that specific brain pro-opiomelanocortin gene products modulate gastric mucosal integrity in response to stress.

Feeding the premature and compromised infant: gastrointestinal considerations

We have presented the current concepts of gastrointestinal ontogeny--the various factors governing the ontogeny of the gastrointestinal tract and the interaction and intricate relationship between different determinants. It is only through a better understanding of the development of the gut and the various factors affecting it that pediatric gastroenterologists are able to design nutritional support strategies for managing very young and compromised neonates.

Influence of thyroid states on stress gastric ulcer formation

Thyroid hormones exert a critical developmental and regulatory role on the morphology and biochemistry of gastrointestinal mucosal cells. However, the relationship between thyroid function and stress gastric lesion formation remains undetermined. This study was designed to test the hypothesis that thyroid states may affect the acute development of gastric lesions induced by cold-restraint stress. Normal (euthyroid), hyperthyroid (200 micrograms of T4 i.p. x 7 days) and hypothyroid (thyroidectomized) rats were used. Gastric lesion incidence and severity was significantly (p less than 0.05) increased in hypothyroid rats, whereas in contrast hyperthyroid rats developed significantly less gastric lesions. As anticipated, plasma levels of thyroxin (T4) were significantly (p less than 0.01) elevated in hyperthyroid rats, and undetectable in hypothyroid rats. Acute pretreatment with i.p. cimetidine (100 mg/Kg), but not T4 (200 micrograms/Kg) 1 h prior to stress completely prevented gastric lesions formation in hypothyroid rats. Finally, binding of 3H-dihydroalprenolol to beta-adrenergic receptors on brain membranes prepared from frontal cortex was reduced by 20% in hypothyroid rats after 3 h of stress. These and other data contained herein suggest that thyroid hormones contribute to modulate the responsiveness of the gastric mucosa to stress. The increased rate of ulcerogenesis observed in hypothyroid rats appears to be mediated by gastric acid secretion. The central mechanism of this response may involve decreased brain nonadrenergic receptor function.

Effect of hypophysectomy, adrenalectomy, pituitary hormone secretion and gastric acid secretion on neurotensin induced gastric protection against stress gastric lesions

In previous studies we have established that intracisternal (i.c.) but not peripheral (intravenous) administration of neurotensin (NT), a brain and gastrointestinal tridecapeptide, totally prevents the development of gastric lesions produced by cold-restraint stress (CRS) with food-deprived rats. In this investigation, removal of the pituitary and adrenal gland, anterior pituitary hormone secretion and gastric acid secretion were evaluated independently as potential intermediates for NT's protective effect. NT (30 micrograms) produced a significant reduction of gastric lesions incidence and severity in intact and sham-operated controls. Adrenalectomy, but not hypophysectomy totally blocked the protective effect of i.c. NT. In addition, replacement therapy with s.c. prednisone (1 mg/kg) for 5 days following adrenalectomy did not restore the protective activity of central (i.c.) NT in adrenalectomized rats. A significant reduction of serum levels of TSH, PRL and GH following i.c. NT (30 micrograms) was observed after 2h of CRS. The gastrosecretory studies revealed that i.c. NT (30 micrograms) did not affect gastric acid secretion in pylorus ligated rats. However, blockade of peripheral (gut) cholinergic (muscarinic) receptors with i.p. atropine methylbromide (1 mg/kg) significantly raised gastric pH and reduced gastric acid concentration and output. In conclusion, the results of this study indicate that the acute protective effect of brain NT appears to be mediated, at least in part, by the sympathoadrenomedullary axis, and not by the pituitary gland or substances derived from the pituitary or by inhibition of gastric acid secretion.

Further observations concerning the effects of hypophysectomy on the gastric mucosa of the rat

Hypophysectomy in rats markedly reduced the weight and surface area of the stomach as well as the volume (mass) of the gastric mucosa and the total parietal and total peptic cell populations. The parietal cell population was reduced by about 50%, and this effect was due entirely to the reduction that occurred in the total surface area of the stomach (50%); the average number of parietal cells per unit area, which reflects the number of parietal cells in the gastric glands, was not affected. The peptic cell population was reduced by about 90%, the factors responsible being a reduction in the average number of peptic cells per unit area (70%) as well as the reduction that occurred in the surface area of the stomach. The disproportionate effect of hypophysectomy on the cell populations was thus due to the reduction in the number of peptic cells per unit area; this effect implies that hypophysectomy had caused a reduction in the number of the peptic cells in the gastric glands.Whatever the mechanisms involved these results were due to a direct effect of pituitary deprivation on the stomach, since they could not be accounted for simply by the inhibition of somatic growth that follows hypophysectomy in rats. Thus the experiment included a group of sham hypophysectomized rats whose somatic growth was inhibited to the same extent as that of the hypophysectomized animals by deliberate underfeeding. While underfeeding reduced the surface area of the stomach (20%) and the total peptic cell population (25%), as well as exerting a marginal effect on the parietal cell population, these effects were much smaller in magnitude than those of hypophysectomy; moreover underfeeding did not affect the number of peptic cells in the gastric glands. The results confirm that the pituitary gland exerts a strong influence on the growth of the gastricmucosa.