Hypothalamic pituitary stimulating and inhibiting hormones

Prostaglandin involvement in hypothalamic control of gonadotropin and prolactin release

Prostaglandin E(2) (PGE(2)) injected into the third ventricle of ovariectomized rats increased plasma luteinizing hormone dramatically and follicle stimulating hormone slightly. PGE(1) elevated prolactin; PGF(1alpha) or PGF(2alpha) had no effect. PGE(2) or PGE(1) injected directly into the anterior pituitary were ineffective. These results suggest that specific prostaglandins act at the hypothalamus to control pituitary hormone release.

Induction of mating behavior in rats by luteinizing hormone-releasing factor

Ovariectomized female rats treated with estrogen, in dosages too low to provoke mating, displayed this behavior when given subcutaneous injections of synthetic luteinizing hormone-releasing factor (LRF) 48 hours later. Two hours after the injection of LRF, components of female sexual behavior appeared. The lordosis reflex followed mounting by the male, and darting and hopping behavior was quite prevalent. On the other hand, treatment with estrogen followed by luteinizing hormone, follicle-stimulating hormone, or thyrotropin-releasing factor did not induce copulatory behavior. The results suggest that LRF may play a role in induction of mating behavior.

Endocrine studies in anencephaly

Endocrine function has been investigated in four anencephalic neonates to determine the influence of absence of cortical and hypothalamic tissue and of hypoplasia of the pituitary. Intravenous glucose administration resulted in higher peak values for blood sugar and more rapid glucose disposal rates than reported in normals. Intravenous insulin tolerance tests on two of the infants failed to evoke elevations in plasma growth hormone, and the infants showed a remarkable resistance to the hypoglycemic effect of insulin. Administration of lysine-vasopressin caused an active growth hormone release. Similarly, there was a large increase in serum thyrotropin after administration of synthetic thyrotropin-releasing hormone. Basal levels of both thyrotropin and growth hormone were low as compared with values reported for normal newborns. Prolactin values obtained on three of the infants were in the normal range. The results strongly suggest that anterior pituitary function mediated by the hypothalamus and its releasing factors is deficient in anencephaly. However, the anterior pituitary can release growth hormone and thyrotropin when stimulated directly and, in the case of thyrotropin release, may function autonomously. The normal prolactin values presumably reflect the absence of the hypothalamic prolactin inhibitory factor.

Alteration of circadian temperature rhythm with third ventricular obstruction

✓ Body temperature and endocrine function were studied in three hydrocephalic patients with tumors in the region of the hypothalamus. A circadian temperature rhythm was present under normal intraventricular pressure but was upset during elevated pressure. The results suggest that the absence of a circadian temperature rhythm in patients with third ventricular neoplasms indicates ventricular obstruction with consequent intracranial pressure and/or hydrocephalus. Conversely, the presence of a circadian temperature rhythm indicates that ventricular obstruction has not occurred or that a shunt system placed to bypass such an obstruction is functioning.

Stimulation of adenosine 3':5'-cyclic monophosphate accumulation in anterior pituitary gland in vitro by synthetic luteinizing hormone-releasing hormone

A near-maximal dose (20 ng/ml) of synthetic luteinizing hormone(LH)-releasing hormone/follicle-stimulating hormone(FSH)-releasing hormone added to incubated anterior pituitary tissue of male rats leads to concomitant increases of intracellular concentrations of adenosine 3':5'-monophosphate and of release of both LH and FSH. The stimulatory effect of LH-releasing hormone/FSH-releasing hormone is observed after a lag period of about 90 min and is progressive at later time intervals; a 3-fold stimulation of cAMP accumulation over control is seen after 210 min of incubation. Half-maximal stimulation of cAMP accumulation is observed between 0.1 and 1.0 ng/ml (0.1-1 nM) of LH-releasing hormone/FSH-releasing hormone. In the presence of 10 mM theophylline, the stimulatory effect of LH-releasing hormone/FSH-releasing hormone on cAMP accumulation is similar to that observed in the absence of the inhibitor of cyclic nucleotide phosphodiesterase, indicating that the releasing hormone exerts its effect by specific activation of adenylate cyclase in LH- and FSH-secreting cells rather than by inhibition of cyclic nucleotide phosphodiesterase. Since the release of growth hormone, thyrotropin, prolactin, and adrenocorticotropic hormone is not affected by LH-releasing hormone/FSH-releasing hormone, and since cAMP stimulates the release of all six adenohypophyseal hormones. the observed changes of cAMP concentrations indicate specific stimulation of adenylate cyclase activity in LH-and FSH-secreting cells of the adenohypophysis.

The biosynthesis, intracellular transport, and packaging of melanocyte-stimulating peptides in the amphibian pars intermedia

Experiments in which glycine-(3)H has been introduced into excised neurointermediate lobes of Xenopus laevis incubated in a modified Krebs-Ringer bicarbonate medium have shown that approximately 50% of the incorporated radioactivity is present in small peptides which have an electrophoretic mobility characteristic of the melanocyte-stimulating (MSH) peptides shown to be elaborated within the tissue. Based on these results and the demonstration that a discrete approximately 7 min pulse of the label can be introduced into the tissue, electron microscope radioautography has been employed to follow the subcellular events concerned with the synthesis, intracellular transport, and packaging of the labeled secretory product. Together, these studies indicate that the newly synthesized material arises in peptide form, rather than as part of a larger prohormone molecule, on the ribosomes of the rough endoplasmic reticulum within the parenchymal cells of the intermediate portion of the lobe. A proportion is then incorporated into and remains for an extended period within the intracisternal granules which are a feature of the rough endoplasmic reticulum within these cells in vitro Most ( approximately 60%) of the labeled secretory product, however, is transferred to the Golgi complex within 30 min and, within a further 10 min, becomes packaged into small ( approximately 200 mmicro) electron-opaque secretory granules. It is probable that under the conditions employed these granules represent the final intracellular location of secretory product before it is released

Binding of thyrotropin-releasing hormone to plasma membranes of bovine anterior pituitary gland (hormone receptor-adenylate cyclase-equilibrium constant-( 3 H)thyrotropin)

An assay for the binding of [(3)H]thyrotropin-releasing hormone ([(3)H]TRH) is described. Plasma membranes isolated from bovine anterior pituitary gland bind about 600 femtomoles of this hormone per mg of protein, as compared to 15 femtomoles per mg of protein in the total adenohypophyseal homogenate (40-fold purification). The equilibrium constant of membrane receptor-[(3)H]TRH binding at 0 degrees C is 4.3 x 10(7) L.M(-1), or a half-maximal binding of this hormone at 23 nM. The binding is time-dependent; addition of unlabeled hormone induces dissociation of the receptor-[(3)H]TRH complex with a half-life of 14 min. The binding of TRH is not altered by 10 muM melanocyte-stimulating hormone-release inhibiting hormone, lysine-vasopressin, adrenocorticotropin, growth hormone, prolactin, luteinizing hormone, insulin, glucagon, L-thyroxine, or L-triiodothyronine. K(+) and Mg(++) increase formation of the receptor-TRH complex at optimal concentrations of 5-25 mM and 0.5-2.5 mM, respectively, with inhibition at higher concentrations. Ca(++) inhibits binding of TRH at all concentrations tested.

Effect of thyrotropin-releasing factor on serum thyroid-stimulating hormone. An approach to distinguishing hypothalamic from pituitary forms of idiopathic hypopituitary dwarfism

To test the hypothesis that the primary defect in some patients with idiopathic hypopituitary dwarfism is failure to secrete hypothalamic hypophysiotropic-releasing factors, synthetic thyrotropin-releasing factor (TRF), 500 mug, wa given intravenously, and timed venous samples obtained for determination of the concentration of plasma TSH by radioimmunoassay in three groups of subjects: (a) 11 patients without evidence of endocrine or systemic disease, (group I) (b) 8 with isolated growth hormone deficiency and normal thyroid function, (group II) and (c) 9 patients with idiopathic hypopituitary dwarfism and thyroid-stimulating hormone (TSH) deficiency (group III). The mean fasting plasma TSH value was 4.1 muU/ml in group I, and 3.9 muU/ml in group II; in both groups there was a brisk rise in plasma TSH to peak levels of 12-45 muU/ml at 30-45 min, and a fall toward base line levels at 120 min. All children in group III had basal TSH levels of < 1.5 muU/ml; one failed to respond to TRF; eight exhibited a rise in plasma TSH with peak values comparable with those in groups I and II. In four of eight children in group III who responded to TRF, the TSH response was delayed and the initial rise in plasma TSH was not detectable until 10-60 min. In these four patients, plasma TSH levels continued to rise at 120 min. The mean fasting concentration of plasma thyroxine iodide (T(4)) in subjects with normal thyroid function (groups I and II) was 5.6 mug/100 ml, and the mean plasma T(4) level at 120 min was 6.6 mug/100 ml. This difference between fasting and postTRF plasma T(4) was significant (P < 0.001) by paired analysis. Mean fasting plasma T(4) concentration in group III patients was 1.3 mug/100 ml; after TRF a significant rise in T(4) concentration was not detected in this group. The results indicate that TRF test is useful in distinguishing between primary hypothalamic and pituitary forms of TSH deficiency. In light of the evidence of TRF deficiency in eight of nine patients with idiopathic hypopituitary dwarfism, it seems likely that in these patients, other pituitary hormone deficiencies may be attributable to deficiency of their respective releasing factors.

The effect of administration of human growth hormone on the plasma growth hormone, cortisol, glucose, and free fatty acid response to insulin: evidence for growth hormone autoregulation in man

The effect of administration of human growth hormone (HGH) (3 mg every 6 hr for 6 days) on the endogenous GH response to insulin-induced hypoglycemia at 8, 12, 24, and 48 hr posttreatment was studied in 11 healthy male adults. Free fatty acid, cortisol, and glucose responses pre- and posttreatment with HGH were evaluated concurrently. Control subjects received saline injections to evaluate relationship of GH responses to the periodicity of insulin tolerance tests. The data were compared for each subject pre- and posttreatment with HGH as well as by comparison of the results of the saline-treated group with those of the HGH-treated group. The mean maximal GH concentration in response to insulin-induced hypoglycemia for all the subjects (n = 16) was 31.1 +/-3.6 ng/ml (+/-SEM) on day 1 of the control period and 23.4 +/-3.1 (SEM) on day 2, not statistically significant.A significant decrease in the maximal peak GH response (n = 8) after insulin-induced hypoglycemia was observed at 8 and 12 hr after HGH administration was terminated with mean peak values for GH of 4.6 +/-1.3 ng/ml and 10.4 +/-1.9 ng/ml, respectively (P < 0.01). A progressive return to control values was noted between 12 and 24 hr. The GH responsiveness of the saline-treated group (n = 5) was unchanged from that observed during the control period. The fasting glucose values were unchanged in the GH-treated group from those of the control period or of the saline-treated controls. Insulin resistance was apparent at 8 hr posttreatment with HGH. No differences in FFA response after insulin-induced hypoglycemia were observed in GH-treated or saline-treated subjects. The rise in plasma cortisol after insulin-induced hypoglycemia was comparable in the GH-treated and saline-treated group. Diurnal variation in plasma cortisol was maintained during the period of GH suppression. These observations support the concept that GH can modulate its secretion by means of an auto-feedback mechanism.