Effect of hypoxia on parathyroid hormone in lactating and neonatal rats: interaction with halothane

Effects of anesthetic agents on serum parathyroid hormone and calcium concentrations in mice

OBJECTIVE

To determine the effects of three anesthetic regimens on serum calcium and parathyroid hormone (PTH) in mice.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Twenty-seven, 12-week-old, FVB mice.

METHODS

Mice were anesthetized with either isoflurane, a combination of ketamine plus xylazine (100 and 10 mg kg(-1), respectively) or ketamine alone (100 mg kg(-1)). Blood was collected before and after the induction of anesthesia. Serum calcium and PTH concentrations were measured and compared.

RESULTS

Isoflurane or ketamine did not significantly alter either serum calcium or serum PTH concentrations. A combination of ketamine plus xylazine significantly increased serum PTH, but not serum calcium concentrations.

CONCLUSIONS

A combination of ketamine and xylazine should be avoided prior to collection of blood for measurement of serum PTH concentrations. Isoflurane is suitable for this purpose.

Augmented hypothalamic corticotrophin-releasing hormone mRNA and corticosterone responses to stress in adult rats exposed to perinatal hypoxia

Stressful events before or just after parturition alter the subsequent phenotypical response to stress in a general process termed programming. Hypoxia during the period before and during parturition, and in the postnatal period, is one of the most common causes of perinatal distress, morbidity, and mortality. We have found that perinatal hypoxia (prenatal day 19 to postnatal day 14) augmented the corticosterone response to stress and increased basal corticotrophin-releasing hormone (CRH) mRNA levels in the parvocellular portion of the paraventricular nucleus (PVN) in 6-month-old rats. There was no effect on the levels of hypothalamic parvocellular PVN vasopressin mRNA, anterior pituitary pro-opiomelanocortin or CRH receptor-1 mRNA, or hippocampus glucocorticoid receptor mRNA. We conclude that hypoxia spanning the period just before and for several weeks after parturition programmes the hypothalamic-pituitary-adrenal axis to hyper-respond to acute stress in adulthood, probably as a result of drive from the parvocellular CRH neurones.

Adiponectin and resistin in the neonatal rat: effects of dexamethasone and hypoxia

Hypoxia is a common neonatal stress that induces insulin resistance and a decrease in body weight gain. Dexamethasone is often used to treat neonatal cardiopulmonary disease, and also leads to insulin resistance and a decrease in body weight gain. The current study addressed the hypothesis that serum concentrations of the adipokines adiponectin and/or resistin are altered during hypoxia and/or dexamethasone therapy in neonatal rats. Rat pups with their lactating dams were exposed to hypoxia (11% O2) from birth and treated with a tapering regimen of dexamethasone from postnatal day (PD) 3-6. Serum adiponectin and resistin were measured on PD7. Hypoxia and dexamethasone independently decreased body weight gain and increased adiponectin levels. The combination of hypoxia and dexamethasone did not further increase adiponectin. Dexamethasone caused a small increase in resistin in normoxic pups, which may facilitate the hyperinsulemic- normoglycemic state we previously described. We also conclude that adiponectin is increased during hypoxia in response to a decrease in the sensitivity to insulin.

Basal and adrenocorticotropin-stimulated corticosterone in the neonatal rat exposed to hypoxia from birth: modulation by chemical sympathectomy

We previously demonstrated that 7-d-old rat pups exposed to hypoxia from birth exhibit ACTH-independent increases in corticosterone associated with an increase in steroidogenic acute regulatory (StAR) and peripheral-type benzodiazepine receptor (PBR) proteins. The purpose of the present study was to determine whether this increase in corticosterone could be attenuated by chemical sympathectomy induced with guanethidine treatment. Rat pups were exposed to normoxia or hypoxia from birth and treated with vehicle or guanethidine and studied at 7 d of age. Hypoxia per se resulted in an increase in plasma corticosterone without a change in plasma ACTH. Guanethidine treatment attenuated the increase in basal corticosterone in hypoxic pups but did not attenuate ACTH-stimulated corticosterone production. This effect was specific as basal and ACTH-stimulated aldosterone was not affected. Guanethidine also attenuated the increase in StAR protein induced by hypoxia. Neither the effect of hypoxia nor that of guanethidine could be explained by changes in the levels of adrenal tyrosine hydroxylase, StAR, or P450scc mRNA, adrenal tyrosine hydroxylase immunohistochemistry, or adrenal catecholamine content. We conclude that chemical sympathectomy normalizes basal corticosterone levels but has no effect on ACTH-stimulated corticosterone levels in 7-d-old rats exposed to hypoxia from birth. The mechanism of the effect of guanethidine to normalize hypoxia-stimulated basal corticosterone remains to be identified, although StAR protein may be an important mediator. This ACTH-independent increase in corticosterone may be a mechanism by which the neonate can increase circulating glucocorticoids necessary for survival while bypassing the hyporesponsiveness of the neonatal hypothalamic-pituitary-adrenal axis.

Effects of hypoxia on the development of intestinal enzymes in neonatal and juvenile rats

Hypoxia in the neonate is known to alter the activity of hepatic and pancreatic enzymes involved in lipid and carbohydrate metabolism. The purpose of this study was to evaluate the effect of neonatal hypoxia on the activity of intestinal enzymes, and to determine whether the administration of glucocorticoids to neonates can mimic the effects of hypoxia. Hypoxia in neonatal rats (0-7 days) increased protein content, and lactase and maltase activity in the duodenal and the jejunal segments of the small intestine compared with normoxic controls. Hypoxia in juvenile rats (28-35 days) did not change these enzymes. Two weeks after returning hypoxic (0-7 days) pups to normoxia, their body weight remained lower than the age-matched controls. In the group recovering from hypoxia, sucrase, maltase, and leucine aminopeptidase activities were lower in the duodenal and the jejunal segment. Compared with controls, LDH activity was lower only in the jejunal intestine in the group recovering from hypoxia. All enzyme activities returned to control levels 3 weeks after recovery. Neonatal rats treated with dexamethasone had a decrease in body weight, but increases in sucrase and maltase activity in both the duodenal and the jejunal segment. Hypoxia in newborn rats caused a delayed maturation of small intestinal enzymes. Increases in serum glucocorticoids after hypoxic exposure probably do not play a major role in the delayed maturation of the disaccharidase activity in the small intestine.