Hormone Secretion Rate Research Articles

Differential changes in the rate and pattern of follicle-stimulating hormone secretion from pituitaries of cyclic rats superfused in vitro.

To study the dynamics of FSH secretion in vitro, we superfused quartered anterior pituitaries obtained from rats at 1230 h on each day of the 4-day estrous cycle. FSH, and in some cases LH, concentrations were determined in sequential effluent collections. A 10-min pulse of LHRH (8 nM) was given at 2 h or at 2 and 4 h of superfusion. With proestrous pituitaries, both gonadotropins responded with a significant increase in the secretory rate during exposure to LHRH and reached a peak rate within 20 min. For LH, this was followed by an exponential decrease to prestimulus baseline; in sharp contrast, the rate of FSH secretion did not return to the prestimulus level during the remaining 4 h of superfusion. Because of this, the FSH secretory response to LHRH was analyzed for maximal initial secretory rate change and total net amount secreted. During the estrous cycle, the initial FSH rate change in response to the first LHRH pulse was low on the days of diestrus and high on proestrus and estrus; with estrous pituitaries, the elevated rate was not sustained, resulting in a reduction in the net amount of FSH secreted. The LHRH self-priming response for FSH was present for pituitaries from each day of the cycle except estrus. Estradiol (50 pg/ml) suppressed both the initial rate change and the net amount secreted in response to the first LHRH pulse, but did not prevent the primed response for FSH. Progesterone (50 ng/ ml) augmented the initial rate change only, and cycloheximide inhibited this effect. Cycloheximide had no effect on the maximal initial FSH secretory rate change in the absence of steroids, but reduced the net amount secreted in response to the first LHRH pulse and eliminated LHRH self-priming. These results 1) provide evidence for two separate components of the FSH secretory response, an initial rate change and a sustained elevated secretory rate, which vary independently, and 2) demonstrate a fundamental difference between LHRH-induced FSH and LH secretion from proestrous pituitaries, in that elevated FSH secretion is sustained for several hours, while LH returns to baseline. The dissimilarities in the requirement for the continual presence of LHRH in vitro could represent the basis for the in vivo differences in the periovulatory FSH and LH surges.

Parathyroid gland response to epinephrine: a rate-sensitivity mechanism.

A model for parathyroid gland response to an epinephrine infusion is proposed. It is based on direct measurements of the parathyroid hormone (PTH) secretion rate as measured directly after cannulation of the venous drainage of single superior parathyroid glands of calves. When epinephrine was infused into a jugular vein, a large increase of PTH secretion rate was observed at the beginning of the infusion. The PTH secretion rate thereafter fell, but it was still significantly above the control rate. At the end of the epinephrine infusion a sharp decrease was observed when the infusion was terminated. These observations are consistent with a rate-sensitive control mechanism. Calculation of the parameters yielded a model, which was then linked with a kinetic model for PTH distribution. Simulation studies were undertaken to predict plasma PTH concentration in response to an epinephrine infusion. Good agreement was found between predicted results and previously published work. The role of this rate-sensitive mechanism in the parathyroid gland is discussed.

Model for parathyroid hormone secretion and metabolism in calves.

A model for parathyroid gland response to differing calcium and magnesium concentrations is proposed based on direct determinations of parathyroid hormone (PTH) secretion rate. A proportional control seems adequate for physiological variations of calcium and magnesium levels. At extreme hypocalcemia, nonlinearities are observed: a model involving the depletion of a storage compartment is proposed, the size of which is calculated. PTH distribution was studied in another group of animals; sampling was made from the saphenous artery and the thoracic duct. Concentrations of plasma and lymph-intact PTH and carboxy-terminal fragments were determined by means of two different radioimmunoassays. The analysis of the results leads to the formulation of a five-compartment model, which shows that the metabolism of intact PTH is only partly due to the formation of carboxy-terminal fragments, most being directly secreted or catabolized. Linking these models for secretion and distribution of PTH, simulation studies were undertaken and compared with published data. This model is then discussed in comparison with previous work concerning other polypeptide hormones.

Dirofilaria immitis in Stray Dogs from Richmond County, Georgia

may be involved. Heat stress is known to evoke a particular set of physiological responses by the host animals. These responses involve changes in hormonal secretion rates and also in the blood vascular system, both of which would cause considerable change in the environment of bloodstream-dwelling parasites. Further work is needed to relate parasitemias to these changes under different stress situations.

Pancreatic neuroendocrinology: peripheral neural mechanisms in the regulation of the Islets of Langerhans.

The islets of Langerhans are richly vascularized and both the islet cells and blood vessels are intimately associated with a variety of autonomic nerves. Direct electrical stimulation of the nerves in vivo or pharmacological stimulation of the islets with neurotransmitters in vitro results in changes in the rate of release of islet hormones. The purpose of this paper is to describe the anatomy of the islet in relation to its vascular supply and both motor and sensory autonomic nerves, which may play a role in altering the secretion rate of islet hormones. Evidence for catecholaminergic, cholinergic, and peptidergic nerves as well as possible peptide neurotransmitters in the pancreas is examined. Secondly, physiological and pharmacological studies are reviewed that reveal how efferent autonomic neural activity leads to altered islet secretion rates. Third, because the complex structure of the islet is supplied with a variety of autonomic nerves, the evidence for excitation of these nerves via reflex activa...

A detailed in vitro characterization of the basal follicle-stimulating hormone and luteinizing hormone secretion rates during the rat four-day estrous cycle.

Studies were undertaken to determine the relative basal anterior pituitary gland FSH and LH release rates in vitro for rats killed by decapitation at 1 of 15 times during the 4- day estrous cycle and to ascertain if these basal release rates correlated with changes in serum gonadotropin concentrations. Trunk blood was collected, and serum was assayed for FSH and LH. Half of the anterior pituitary gland was homogenized and assayed for FSH and LH. The other half was placed in culture medium for a 30-min preincubation and then placed in fresh media for a 2-h incubation (basal FSH and LH release). Serum FSH concentration rose in association with a rise in serum LH levels during the afternoon of proestrus (first phase of FSH release). Whereas serum LH levels fell during the evening of proestrus, the serum FSH concentration remained elevated through 2400 h on estrus (second phase of FSH release). The basal FSH release into medium increased markedly during late proestrus and showed a highly significant positive ...

Inhibition by somatostatin of bovine growth hormone secretion following sodium channel activation.

1. Growth hormone secretion, exchangeable cellular sodium and calcium concentrations measured by 22Na and 45Ca incorporation, and efflux of 45Ca were studied in dispersed bovine anterior pituitary cells. 2. Addition of veratridine (100 microM), an activator of sodium channels, increased exchangeable sodium and calcium concentrations in the cells, the efflux of 45Ca from prelabelled cells, and caused a biphasic stimulation of the rate of growth hormone secretion. Secretion of growth hormone was not stimulated when the extracellular calcium was decreased below 0.1 mM. 3. The increases in growth hormone secretion, exchangeable calcium concentration and 45Ca efflux from prelabelled cells caused by veratridine were abolished by addition of the calcium antagonist verapamil (20 microM). Verapamil also reduced the rise in exchangeable sodium caused by veratridine and increased the resting exchangeable sodium concentrations. 4. The peptide somatostatin (1 micrograms/ml) prevented veratridine-stimulated growth hormone secretion but did not inhibit the increases in exchangeable sodium and calcium caused by veratridine. The peptide itself elicited a transient increase in 45Ca efflux and subsequently partially inhibited veratridine-stimulated 45Ca efflux. 5. The data suggest that anterior pituitary cells possess voltage-sensitive sodium channels. Activation of these channels by veratridine may lead to depolarization and increased entry of calcium via potential-dependent calcium channels, which contributes to a rise in cytoplasmic calcium concentration and the subsequent stimulation of growth hormone secretion. We conclude that the calcium antagonist verapamil may also interact with sodium channels, and that the peptide somatostatin may act on growth-hormone-secreting cells either to prevent the rise in cytoplasmic calcium by hyperpolarizing the cells or to decrease the affinity of a population of calcium binding sites in the cells.

Thyroid blood flow rate in man. Electromagnetic flowmetry during operation in euthyroid normal gland, nontoxic goiter, and hyperthyroidism.

Human thyroid blood flow rate (TBF) was measured during operations by electromagnetic flowmetry in 75 euthyroid patients with normal thyroid tissue, nodular goiter, or solitary adenoma, and in 22 hyperthyroid patients with diffuse or nodular goiter. Blood flow rate was measured in one to four of the thyroid arteries. No difference in blood flow rate was seen between the left and right lobes. The slight difference found between the inferior and superior arteries was not significant. In each subject, total TBF was calculated as 4 times the mean of the recorded blood flow in the single arteries. The total TBF was 31 (9-109) ml/min (inner 95 percentile range) in euthyroid patients, similar in all 3 groups. This is less than in most earlier reports. The relative TBF was 1.2 (0.4-3.8) ml/min/g thyroid tissue in normal thyroid tissue and 0.6 (0.1-3.7) ml/min/g in nontoxic nodular goiter (p less than 0.01). Patients with hyperthyroidism had a higher total TBF 54 (15-197) ml/Min (p less than 0.001), despite preoperative treatment giving euthyroidism, Similar TBF rates were found in 3 hyperthyroid patients given propranolol preoperatively. Electromagnetic flowmetry is applicable to study thyroid blood flow rate. Human TBF shows considerable interindividual variations, which must be kept in mind when studying directly the rate of thyroid hormone secretion from arteriovenous gradients.

DNA Characteristics of Human Pituitary Tumours

Biopsies from pituitary tumours in 8 patients were analysed with DNA flow-cytofluorometry immediately after surgery and after organ culture. Good agreement was found between the degrees of ploidy and of the relative proportions of cells in different phases of the cell cycle, indicating a good stability and reproducibility of pituitary tumour explants in vitro. Analysis of DNA content indicated a homogeneous cell population in tumours before and after explantation. No apparent correlation was observed between hormone secretion rate in diploid and aneuploid tumours, respectively, and DNA characteristics.

Plasma corticosteroids in marine, terrestrial and freshwater snakes

1. 1. Plasma concentrations of corticosterone and aldosterone were measured in plasmas of marine, terrestrial and freshwater snakes by competitive protein-binding and radioimmunoassay respectively. 2. 2. A broad range of both corticosterone (from below 1.0 ng/ml to above 400 ng/ml plasma) and aldosterone (0.8 ng/ml to 54.1 ng/ml plasma) concentrations were recorded. 3. 3. No overt correlation between plasma corticosteroid status or adrenal gland weight and habitat type could be discerned, but seasonal factors and possibly differing hormone secretion rates prevent firm conclusions from being drawn.

A reappraisal of the goitre-prevention assay: Determination of the thyroid secretion rate in the Japanese quail and the relative potencies of T 3 and T 4 in preventing goitrogenesis

This reappraisal shows that the goitre-prevention assay (GPA) is as effective as radiometric techniques for estimating thyroid hormone secretion rates (TSR) in quails ( Coturnix coturnix japonica) and can be used where cost or facilities preclude the use of radioisotopes. A simple modification of GPA results analysis is described which enables calculation of confidence limits of the estimated TSR. Birds were injected subcutaneously twice daily for 20 days with 0.5 ml 0.9% (w/v) NaCl/100 g body wt/day alone (controls) or containing a fixed dose of goitrogen (10 mg 6- n-2-propylthiouracil (PTU)/100 g body wt/day) combined with one of several doses (1.4, 2.1, 2.8, 3.5 μg/100 g body wt/day) of either l-triiodothyronine (T 3) or l-thyroxine (T 4). Thyroid weights (per 100 g body wt) were measured after decapitation on the 21st day. The goitre-preventive doses of T 3 or T 4 (referred to as TRSs) were estimated as the y-intercepts from linear regressions of T 3 or T 4 doses on the differences between the mean thyroid weight of control birds and thyroid weights of PTU-treated birds; TRSs ± 95% confidence limits were 1.81 ± 0.15 (df = 14) for T 3 and 1.67 ± 0.13 (14) μg/100 g body wt/day for T 4.

Role of the heterogeneity of thyroglobulin in the secretion of thyroid hormone in mice.

The rates of thyroglobulin hydrolysis and iodothyroine release from mouse thyroid glands were studied in vitro. Recently iodinated thyroglobulin ('new pool') had been labelled during life by injection of 131I 3 h before removal of the thyroid, 'old pool' thyroglobulin had been labelled by the administration of 125I in the drinking water for 1 week starting 3 weeks earlier. Chromatogrphic analysis of pronase digests of the thyroid glands showed that the iodothyronine content of the old and new pools were 19.5 and 7.4 per cent respectively. In the basal state the rate of thyroglobulin hydrolysis was lower from the old pool but the rate of hormone secretion was similar from both pools. Thyrotrophin (TSH) increased the rate of thyroglobulin hydrolysis and hormone release from both pools by up to four to six times the basal rate, the effect being maximal 2 h after administration of TSH and lasting for 6-8 h. The rate of thyroglobulin hydrolysis after TSH was similar in both pools but the rate of release of labelled iodothyronines was significantly higher from from the old pool. These studies have indicated that although hydrolysis of thyroglobulin paroceeds faster in the new pool than in the old ('last come, first served' hypothesis) neverrtheless there is no difference in the rate of hormone secretion from the two pools, and hydrolysis in both pools is affected by TSH.

Acclimation of mousedeer ( Tragulus javanicus) to hot temperature: Changes in thyroid activity

Abstract o 1. Thyroid hormone concentrations and secretion rate of Tragulus javanicus exposed to 27 and 33°C were measured. 2. Serum levels of T3 and T4 were 0.47±0.06 ng/ml (mean±SEM) and 36.2±2.3 ng/ml ( N =8) respectively. The values were lower at 33°C. 3. Thyroid secretion rate was also decreased by the higher ambient temperature.

Effect of epinephrine on parathyroid hormone secretion in calves.

The effect of epinephrine on parathyroid hormone (PTH) secretion rate and the molecular nature of immunoreactivity in parathyroid venous blood was assessed in seven anesthetized calves. PTH secretion rate was measured by a technique which involved RIA of parathyroid venous blood that was collected during timed intervals and measured volumetrically. The molecular nature of immunoreactivity in parathyroid venous plasma was evaluated by gel column chromatography and RIAs which recognized specific regions of the PTH molecule, i.e. the amino-terminus or carboxyl-terminus. Plasma calcium concentration was measured by chelometric titration. Epinephrine HCI was infused iv into a normocalcemic calf at rates of 0.025, 0.05, 0.10, 0.25, and 0.40 μg/kg-min. PTH secretion rate progressively increased in response to increased rates of infusion until a near maximal secretion rate was attained at an infusion rate of 0.25 μg/kg-min. Epinephrine HCI was infused iv into five calves at a rate of 0.25 μg/kg-min during and aft...

Altered parathyroid response to calcium in hypercalcemic neonatal calves.

Calves are born with hypercalcemia which recedes within 2–3 weeks. To assess the role of the parathyroids in this condition, immunoreactive parathyroid hormone (iPTH) secretion rate was measured during induced alterations of plasma calcium concentration in six anesthetized calves which were 1–3 days of age. The technique involved RIA of parathyroid venous blood which was collected during timed intervals and measured volumetrically. Elevation of plasma calcium concentration decreased PTH secretion rate but above 12 mg/100 ml, a nonsuppressible rate of secretion was maintained despite any further increase in plasma calcium concentration. Between 9.5–12 mg/100 ml, iPTH secretion rate and plasma calcium concentration were inversely related. A maximal rate of secretion was attained when plasma calcium concentration was reduced to 9.5 mg/100 ml, and it did not increase when plasma calcium was reduced to a lower level. The sigmoid relationship between iPTH secretion rate and plasma calcium conce ntration is simi...

C-Peptide Secretion During the Remission Phase of Juvenile Diabetes

C-peptide secretion was studied in eight juvenile diabetics during the remission phase of the disease. The release of C-peptide was measured after a (1) normal intravenous glucose tolerance test, (2) a double glucose tolerance test, (3) an arginine infusion, and (4) after an intravenous glucose tolerance test followed by an arginine infusion. Under all conditions the intravenous glucose load had only a minimal effect on the secretion of C-peptide, while arginine alone or after the intravenous glucose tolerance test stimulated the release of the peptide in all patients. Pretreatment with glucose did not augment the effect of arginine on C-peptide release. The results indicate that during the remission phase of juvenile-onset diabetes the endocrine pancreas does not recognize glucose as and appropriate signal for C-peptide release and cannot transform the amplifying effect of glucose into a higher hormonal secretion rate.

Sigmoidal relationship between parathyroid hormone secretion rate and plasma calcium concentration in calves.

Parathyroid hormone (PTH) secretion rate was measured in 16 anesthetized calves by using a technique involving radioimmunoassay of parathyroid venous blood which was collected during timed intervals and measured volumetrically. The calves ranged in age from 2-14 weeks. Plasma calcium concentration was altered by infusion of solutions of CaCl2 or disodium ethylenediamine tetracetate (Na2 EDTA) into the jugular vein. When plasma calcium concentrations exceeded 10.5 mg/100 ml, a basal, non-suppressible secretion rate of 0.3 ng/kg/min was maintained despite the induction of hypercalcemia. Slight changes in secretion rate were observed in response to changes of plasma calcium in the range between 9 and 10.5 mg/100 ml. Below 9 mg/100 ml, a small decrease in plasma calcium concentration evoked a pronounced increase in secretion rate. A maximal secretion rate of about 5.5 ng/kg/min was attained at a plasma calcium concentration of approximately 7.5 mg/100 ml and it was not increased by more severe hypocalcemia. These observations confirm the sigmoidal relationship between PTH secretion rate and plasma calcium concentration which was previously suggested by measurement of PTH concentration in peripheral plasma of hypocalcemic, parturient cows.

An Estimation of the Parathyroid Hormone Secretion Rate in Vitamin D Deficient Rats

In an attempt to define the rate of endogenous secretion of parathyroid hormone in vitamin D deficiency, graded amounts of hormone were infused constantly into vitamin D deficient and vitamin D fed acutely thyroparathyroidectomized rats in a perfusion balance study. The dose of hormone needed to compensate for acute thyroparathyroidectomy was estimated. Serum levels of calcium and phosphorus, renal clearances of phosphorus and urinary excretion of cyclic AMP, each determined 16 hr after the surgery, were employed as parameters of the hormone effect. It was concluded that, in the condition of the perfusion balance study, the secretion rate of parathyroid hormone was 5.1-8.6 USP u/hr in the vitamin D deficient animals compared with 0.81-0.84 USP u/hr in the control.

Contribution of maternal circulation to blood-borne progesterone in the fetus: I. Studies on human subjects

Tritiated progesterone was infused intravenously at a constant rate into three pregnant volunteers in labor, for at least two hours before delivery. Blood samples from a maternal peripheral vein and from umbilical vessels were taken at birth. Comparison of the specific activities of progesterone in these samples indicated that 10 per cent or less of the hormone in fetal circulation is derived from transfer of maternally circulating progesterone. After consideration of reported values of umbilical vein blood flow at term and measured arteriovenous differences in concentrations of progesterone in umbilical vessels, the secretion rate of the placental hormone toward the fetus was estimated to be about 1/10 of the rate of secretion of progesterone toward the maternal circulation. About 1 per cent of the maternally circulating hormone was found to cross the placenta.

Thyroid hormones and metabolic rate in burros, Equus asinus, and llamas, Lama glama: Effects of environmental temperature

1. 1. Rate of oxygen consumption, V 02, and thyroid hormones secretion rate were measured in burros, Equus asinus and llamas. Lama glama. exposed to heat, cold and dehydration. 2. 2. The llama had a lower V 02 than the burro. Exposure to heat for 3–4 days and to dehydration decreased V 02 in both species. 3. 3. Plasma levels of T 4 and T 3 were higher in the llama than in the burro. However, secretion rates of T 4 and T 3 were similar in both species. The discrepancy between thyroid hormonal plasma levels and secretion rates in llamas and burros were due to differences in the disappearance rate (K) of these hormones. 4. 4. The difference in V O 2 between the two species does not seem to be related to thyroid function.