Regulation and substrate specificity of a steroid sulfate-specific hydroxylase system in female rat liver microsomes.
(49/770)
The sulfate-specific hydroxylase system in liver microsomes from rats has been investigated with respect to its substrate specificity. Eighteen different C18, C19, C21, and C27 steroid sulfates and the coresponding free steroids have been incubated with microsomal preparations from male and female rats. The sulfate-specific system was only present in preparations from female rats and primarily catalyzed hydroxylation in position 15beta but also in position 7beta. In contrast to this, male liver microsomes were more efficient than female liver microsomes in hydroxylating free steroids; these were hydroxylated in positions 2alpha,2beta,6alpha,6beta,7alpha,7beta,16alpha, and 18. The sulfate-specific hydroxylase system in female liver microsomes was found to have rigid requirements c concerning the structure of ring D in the substrate molecule; only 17beta-sulfates (C18 and C19 steroids) and 21-sulfates (C21 steroids) were hydroxylated. Less rigid criteria, however, exist concerning the structure of ring A. The following K-m values were determined for microsomal 15beta-hydroxylation: 5alpha-androstane-3alpha,17beta-diol disulfate, 17.2 muM; 5beta-androstane-3alpha,17beta-diol disulfate, 16muM;5alpha-androstane-3alpha,17beta-diol 17-sulfate, 26 muM; and estradiol 17-sulfate, 181 muM. Some of the regulatory mechanism controlling the activity of the sex-specific 15beta-hydroxylase system also have been studied and compared to the mechanism controlling the activities of the less specific 2alpha-, 7alpha-, and 18-hydroxylase systems active on 5alpha-[4-14C]androstane-3alpha,17beta-diol. Biliary drainage did not affect the 15beta-hydroxylase activity, whereas the 2alpha- and 7alpha-hydroxylase activities decreased.. (+info)
Pituitary control of BK potassium channel function and intrinsic firing properties of adrenal chromaffin cells.
(50/770)
The discovery that the hypothalamic-pituitary-adrenocortical (HPA) endocrine stress axis controls an alternative splicing decision in chromaffin Slo-encoded BK (big potassium) channels raised the possibility that activation of the HPA could serve as a mechanism to tune the intrinsic electrical properties of epinephrine-secreting adrenal chromaffin cells. To test this, we compared BK functional properties and cell excitability in chromaffin cells from normal and hypophysectomized (pituitary-ablated) rats. Hypophysectomy was found to alter the voltage dependence and kinetics of BK gating, making channels less accessible for activation from rest. Perforated-patch recordings revealed changes in action potential waveform and repetitive firing properties. The maximum number of spikes that could be elicited with a 2 sec depolarizing current pulse was reduced by approximately 50% by hypophysectomy. The results indicate that pituitary hormones can adapt the mechanics of adrenal catecholamine release by tailoring BK channel function. (+info)
Effect of destruction of the posterior pituitary on the diuresis from left atrial receptors.
(51/770)
1. In anaesthetized dogs, stimulation of atrial receptors after destruction of the pituitary gland results in a diuresis. This response was not abolished by the administration of bretylium tosylate and was also observed in a surgically denervated kidney. 2. The diuresis is qualitatively similar to that observed in anaesthetized dogs with intact pituitary glands. 3. It is concluded that the diuresis which results from stimulation of the left atrial receptors is mediated by a blood-borne agent which is not the antidiuretic hormone. (+info)
Growth hormone stimulation of amino acid transport and utilization by the perfused rat liver.
(52/770)
The effects of growth hormone, administered in vivo or added in vitro, on amino acid transport and utilization have been studied in perfused livers of normal and hypophysectomized rats. A perfusion system employing a nonrecirculating medium was used in all of the studies. Two nonmetalbolizable amino acid analogues, alpha-aminoisobutyric acid (AIB) and 1-aminocyclopentane carboxylic acid (cycloleucine) were used to study transport. Accumulation of AIB increased linearly over a 60-min perfusion period, reaching distribution ratios of between 1 and 2 for both groups of animals. Treatment of both normal and hypophysectomized rats with growth hormone 60 min prior to the start of perfusion increased AIB distribution ratios by up to 84 and 108%, respectively. Accumulation of cycloleucine was linear for only about 20 min of perfusion and then plateaued. Steady state distribution ratios of this analogue ranged between 1 and 2 for both groups of animals. Growth hormone treatment had no apparent effect on the time necessary to reach these steady state levels, but significantly increased them in livers of both normal and hypophysectomized rats by 16 and 42%, respectively. Studies designed to analyze the kinetic properties of these hormone effects revealed that growth hormone treatment caused 2-fold i-crease in the maximum velocities of both the AIB and cycloleucine transport systems. The substrate concentration for half-maximal transport velocity was increased slightly for both systems by growth hormone. Direct effects of growth hormone were demonstrated in studies where livers of hypophysectomized rats were perfused under conditions simulationg those of experiments in which the hormone was administered in vivo. Following an initial 45-min period of perfusion the medium during the 20 min. Growth hormone added to the medium during the entire 65-min perfusion at a concentration of 1 mug per ml caused a 30% increase in the cycloleucine distribution ratio. Under similar experimental conditions growth hormone directly stimulated three hepatic pathways of amino acid utilization: (a) incorporation of [14C]valine into protein, (b) urea formation and (c) conversion of 14-C-amino-acids to labeled glucose. Intracellular concentrations of seven amino acids, including threonine, serine, proline, glycine, alanine, lysine, and arginine, were increased significantly in livers perfused with medium containing growth hormone... (+info)
Effects of hypophysectomy, growth hormone, and thyroxine on protein turnover in heart.
(53/770)
Cardiac atrophy following hypophysectomy was accompanied by decreased heart content of RNA and polysomes and increased levels of ribosomal subunits, suggesting that protein synthesis was restricted by a reduced supply of ribosomes and an imbalance between rates of peptide-chain initiation and elongation. During perfusion in vitro, provision of palmitate restored the normal balance between rates of initiation and elongation but protein synthesis was lower in hearts of hypophysectomized than normal rats, reflecting the lower RNA content of hearts from hormone-deficient animals. After the period of atrophy had passed, or after treatment with growth hormone and thyroxine, heart RNA content and rates of protein synthesis were equal to or greater than those found in normal hearts. When plasma levels of amino acids, glucose, fatty acids, and insulin, and rates of beating and ventricular pressure development observed in normal and hypophysectomized rats were simulated during in vitro perfusion, hearts from hormone-deficient rats had reduced rates of protein synthesis but unaltered rates of degradation. Cathepsin D activity in heart homogenates (+ Triton X-100) was elevated during cardiac atrophy when expressed per g of tissue but not when expressed per heart. (+info)
Pituitary adenomas: early postoperative MR imaging after transsphenoidal resection.
(54/770)
BACKGROUND AND PURPOSE: Although there have been several reports on postoperative MR imaging of the sella, immediate postoperative changes (usually within 3 days) have not been extensively analyzed. The purpose of this study was to establish the value of early postoperative MR imaging in differentiating residual tumor from postoperative surgical changes in the sella after transsphenoidal resection of pituitary adenomas. METHODS: Eighty-three patients with surgically proven pituitary adenomas (32 nonfunctioning, 24 prolactin-secreting, 22 growth hormone-secreting, and five prolactin- and growth hormone-secreting tumors) were studied prospectively. All patients underwent dynamic MR imaging within 7 days after surgery. We analyzed the postoperative MR images by focusing on changes in the pituitary gland, signal intensity, resorption of implanted material, and visibility of residual tumor. The patients were divided into four groups according to enhancement pattern of the postoperative pituitary mass: no enhancement, nodular enhancement, peripheral rim enhancement, and a combination of nodular and peripheral rim enhancement. RESULTS: Postoperative changes included resorption of implanted material and reexpansion of the pituitary gland. In 22 patients, residual tumors were found, and all patients showed nodular or combined enhancement. The residual tumors were confirmed by immediate reoperation in three patients, by hormonal assay and follow-up MR images in 11 patients with functioning adenomas, and by growth of the tumor on follow-up MR images in eight patients with nonfunctioning adenomas. Forty-eight patients showed no enhancement and 13 patients showed peripheral rim enhancement. CONCLUSION: Early postoperative dynamic MR imaging after transsphenoidal resection in pituitary adenoma is very effective in differentiating residual tumor from postoperative surgical changes. (+info)
Altered sexual differentiation of hepatic uridine diphosphate glucuronyltransferase by neonatal hormone treatment in rats.
(55/770)
The hepatic microsomal enzyme UDP-glucuronyltransferase undergoes a complex developmental pattern in which enzyme activity is first detectable on the 18th day of gestation in rats. Prepubertal activities are similar for males and females. However, postpubertal sexual differentiation of enzyme activity occurs in which male activities are twice those of females. Neonatal administration of testosterone propionate or diethylstilboestrol to intact animals resulted in lowered UDP-glucuronyltransferase activity in liver microsomal fractions of adult male rats, whereas no changes were observed in the adult females and prepubertal male and female animals. Neonatal administration of testosterone propionate and diethylstilboestrol adversely affected male reproductive-tract development as evidenced by decreased weights of testes, seminal vesicles and ventral prostate. Diethylstilboestrol also markedly decreased spermatogenesis. Hypophysectomy of adult male rats resulted in negative modulation of microsomal UDP-glucuronyltransferase and prevented the sexual differentiation of enzyme activity. In contrast hypophysectomy had no effect on female UDP-glucuronyltransferase activity. A pituitary transplant under the kidney capsule was not capable of reversing the enzyme effects of hypophysectomy, therefore suggesting that the male pituitary factor(s) responsible for positive modulation of UDP-glucuronyltransferase might be under hypothalamic control in the form of a releasing factor. Neonatal testosterone propionate and diethylstilboestrol administration apparently interfered with the normal sequence of postpubertal UDP-glucuronyltransferase sexual differentiation. (+info)
Mature teratoma arising from the sella--case report.
(56/770)
A 26-year-old, short statured, obese male presented with a mature teratoma located entirely within the dural confines of the sella manifesting as headaches and progressive loss of vision. He had panhypopituitarism. Magnetic resonance imaging showed a large sellar-suprasellar but entirely infradiaphragmatic tumor of varying consistency. The tumor was resected through a trans-sphenoidal route. The tumor had elevated the diaphragma sellae to a significant extent but did not pass through. Histological examination confirmed a mature teratoma. (+info)