Jerome M. Hershman

Estrogen replacement therapy by transdermal estradiol administration

To determine whether the nonoral administration of estradiol (E2) might provide physiologic replacement without alteration of hepatic function, 20 postmenopausal women were studied before and after 3 weeks of treatment with either E2-containing transdermal therapeutic systems or placebo. Twenty premenopausal women were also studied. With E2-containing systems, serum E2 and estrone levels were restored to the premenopausal range. Variable responses of the different biochemical and biologic markers of the actions of E2 were observed. The most sensitive marker was vaginal cytology, with the E2 dosage reverting the maturation index to premenopausal values. Hot flashes, measured objectively, were reduced in frequency but not abolished. Serum levels of follicle-stimulating hormone and luteinizing hormone were lowered but remained higher than the premenopausal range. No significant changes were noted in urinary calcium/creatinine and hydroxyproline/creatinine ratios, which were used as markers of bone resorption. With active systems, no significant changes were noted in the concentrations of the hepatic proteins renin substrate and thyroxine-binding globulin or in the binding capacities of cortisol-binding globulin and sex hormone-binding globulin. These results indicate that transdermal E2 administration may be used to provide estrogen replacement while exerting limited effects on hepatic function.

β-Endorphin in male rat reproductive organs

Abstract β-Endorphin and related peptides have been detected within the male rat reproductive system. The β-endorphin immunoreactivity of testis exhibits parallelism with synthetic human β-endorphin on serial dilution and coelutes with β-endorphin on Sephadex G-50 and reverse phase high pressure liquid chromatography. Sephadex G-50 chromatography also indicates the presence of β-lipotropin. β-Endorphin concentrations in rat seminal vesicles and prostate were approximately 25% of that in testis.

High concentrations of p-Glu-His-Pro-NH2 (Thyrotropin-releasing hormone) occur in rat prostate

Thyrotropin-releasing hormone (TRH) immunoreactivity occurs in high concentration within the rat prostate. Previous studies have shown that the immunoreactive species consists of more than one TRH-like tripeptide which cross-reacts in the TRH radioimmunoassay. The component which was highly retained during cation exchange chromatography was subjected to a preparative scale isolation, purification and structural analysis. The methods used included methanol extraction, water-ethyl ether partitioning, cation exchange chromatography, affinity chromatography, high pressure liquid chromatography, TRH radioimmunoassay, in vitro pituitary bioassay, TRH receptor assay, and amino acid analysis. The mean concentration of the predominant amino acids (Glu, His, Pro), 344 pmoles/ml, and the TRH concentration measured by TRH radioimmunoassay prior to acid hydrolysis, 372 pmoles/ml, were nearly identical. Because the material analyzed cochromatographed with synthetic TRH in several chromatographic systems, had a radioreceptor potency which was indistinguishable from that for synthetic TRH, and released TSH and prolactin but not growth hormone from rat pituitaries in vitro, it is concluded that pGlu-His-Pro-NH2 is one of the TRH-like peptides in the rat vental prostate.

Testosterone increases TRH biosynthesis in epididymis but not heart of zinc-deficient rats

Enzymes responsible for the posttranslational processing of precursor proteins to form alpha-amidated peptide hormones require the availability of several cofactors, including zinc, copper, and ascorbic acid. For this reason, we studied the effects of 6 weeks of a zinc-deficient diet (ZD1; 1 microgram zinc per g diet), pair-feeding (PF), and marginal zinc deficiency (ZD6; 6 micrograms zinc per g diet) compared to a control diet (36 micrograms/g zinc) on the conversion of prepro-TRH to TRH in epididymides, testes, prostate, pancreas, and heart of young adult, male Sprague-Dawley rats. In the epididymis, severe zinc deficiency (ZD1 diet) reduced TRH and TRH-like peptides to undetectable levels. In ZD6 animals, TRH was selectively inhibited 80%, while pair-feeding increased all of these peptide levels compared to controls. A similar effect of zinc deficiency on the TRH precursor peptides was observed. A quantitative loss of TRH from the testes of ZD1 was also observed. Zinc deficiency results in a substantial reduction in body weight and testosterone production in male rats. Exogenous testosterone (T) supplementation of ZD1 rats resulted in a selective increase in the TRH concentration of the epididymis but not of the heart. The change in steady-state levels of TRH precursor peptides in the hearts of the ZD1+T rats was consistent with a reduction in the activity of the zinc-dependent carboxypeptidase H enzyme. We conclude that severe zinc deficiency inhibits TRH biosynthesis in reproductive tissues of the male rat due to the combined effects of hypogonadism and inhibition of the zinc-dependent carboxypeptidase H.

Thyroid hormone modulation of TRH precursor levels in rat hypothalamus, pituitary, thyroid and blood

In the present study we have examined the in vivo effects of thyroid hormones and TRH on tissue and blood levels of TRH and TRH-Gly (pGlu-His-Pro-Gly), a TRH precursor. Using specific radioimmunoassays (RIAs), we measured TRH immunoreactivity (TRH-IR) and TRH-Gly-IR concentrations in blood, hypothalamus, anterior and posterior pituitary, and thyroid in euthyroid, hypothyroid and thyroxine (T4)-treated 250 g male Sprague-Dawley rats. TRH-Gly-IR and TRH-IR were detected in all of these tissues. Highly significant positive correlations between whole blood TRH-Gly-IR levels and the corresponding serum TSH values (p less than 0.01), whole blood TRH-IR versus serum TSH (p less than 0.01) and whole blood TRH-Gly-IR versus whole blood TRH-IR (p less than 0.01) are consistent with cosecretion of TRH and TRH precursor peptides into the circulation. Euthyroid rats injected with TRH IP (1 microgram/100 g b.wt.) and hypothyroid rats had 4-fold higher whole blood TRH-Gly-IR levels compared to euthyroid controls (p less than 0.0005). Injection of TRH into euthyroid rats significantly increased the TRH-Gly-IR concentration in the hypothalamus, anterior and posterior pituitary and thyroid. The increase in blood TRH-Gly-IR following intravenous TRH may be due, in part, to partial saturation of TRH-degrading enzymes in blood and cell membranes. The ratio of TRH-Gly to TRH was significantly increased in the anterior pituitary by hypothyroidism and TRH injection, suggesting that thyroid hormones and TRH regulate the alpha-amidation of TRH-Gly to form TRH in this tissue. TRH-Gly levels of pooled pituitary and thyroid extracts quantitated by a combination of TRH-Gly RIA and high performance liquid chromatography (HPLC) revealed several-fold increases following incubation at 60 degrees C. Heating at this temperature may block the alpha-amidation activity in extra-hypothalamic tissues but not the trypsin-like enzymes which cleave prepro-TRH into TRH-Gly-immunoreactive peptides.

Triiodothyronine induces a transferable factor which suppresses TSH secretion in cultured mouse thyrotropic tumor cells

Abstract Modulation of TSH release from mouse thyrotropic tumor cells was studied. T3 (1 nM) inhibited basal TSH release, while 6 nM T3 blocked TRH-induced TSH release. Prior exposure of cells to actinomycin or cycloheximide prevented T3 from suppressing basal and TRH-induced TSH release. The TSH-suppressive activity from T3-treated cells was extracted and exposure of untreated thyrotropic cells to this material resulted in suppression of TSH release. The data suggest that T3 suppression of TSH is mediated by formation of an inhibitory protein in thyrotropic cells.

Osmotic control of the release of prolactin and thyrotropin in euthyroid subjects and patients with pituitary tumors

The effects of acute changes in serum osmolality on basal serum PRL and TSH levels and on responses of prolactin (PRL) and thyrotropin (TSH) to the thyrotropin-releasing hormone (TRH) analogue, N3im-methyl-TRH, were studied in ten euthyroid subjects and in three patients with PRL-secreting pituitary tumors. An oral water load of 20 ml/kg had no effect on basal serum PRL or TSH levels but did result in an increased PRL response to methyl-TRH in the ten euthyroid patients. Intravenous infusion of 5% sodium chloride in the ten euthyroid subjects significantly depressed basal serum PRL levels but had no effect on the PRL response to methyl-TRH. Infusion of hypertonic saline significantly decreased the TSH response to methyl-TRH. In the three patients with pituitary tumors, oral water loading and hypertonic saline infusion had no significant effect on the basal serum PRL and TSH or the PRL and TSH responses to methyl-TRH. The patients with pituitary tumors had a higher basal serum osmolality and a proportionately higher serum concentration of arginine vasopressin than the euthyroid patients. These data suggest that changes in osmolality in euthyroid patients may have a direct effect on the anterior pituitarys PRL and TSH response to a releasing factor.

Thyrotropin-releasing hormone and a homologous peptide in the reproductive system of the female rat and pig

Abstract TRH and a TRH homologous peptide have been shown to occur throughout the female rat and pig reproductive systems by TRH radioimmunoassay, SP-Sephadex C-25 cation exchange chromatography, and parallel line analysis of the assays. The total amount of TRH and TRH homologous peptide immunoreactivity was highest in the oviducts followed by the ovary and then uterus. The concentration of TRH immunoreactivity in all reproductive organs of the rat fell gradually from one month of age. TRH and the TRH homologous peptide were not parallel on serial dilution and measurement in the same TRH radioimmunoassay. The rapid degradation of TRH by pig follicular fluid may explain the higher measured concentration of TRH homologous peptide compared to TRH not only in pig follicular fluid but also in the pig ovary as a whole.

Hypothalamic-Pituitary-Thyroid Axis in Aging

Dietary iodine (I) is essential for synthesis of thyroid hormone (TH). The usual dietary I intake is 150–250 µg/d. Iodine is absorbed in the upper gastrointestinal tract, enters the blood tream, and is actively transported into thyroid cells by the sodium (Na+)/iodide (I-) symporter (NIS), a membrane transport protein. The I- that is not concentrated by the thyroid, is rapidly cleared by the kidneys. The trapped I- is oxidized by thyroid peroxidase and hydrogen peroxide to an unstable intermediate, which is rapidly incorpo-rated into yrosine, to form monoiodotyrosine (MIT) and diiodotyrosine (DIT) in peptide linkage within the thyroglobulin molecule. The iodotyrosines couple to form thyroxine (3,5,3′,5′-tetraiodothyronine, T4) or triiodothyronine (3,5,3′-triiodothyronine, T3), areaction that is also catalyzed by thyroid peroxidase. Once iodinated, thyroglobulin containing newly formed iodothyronines is stored in the follicular lumen. The T4:T3 ratio within the thyroid is about 10.

Relationship of iodide-induced increase in TSH response to TRH to changes in serum thyroid hormones.

Large doses of iodide (500 mg three times a day) administered to normal men for 10--12 days caused a rise in basal serum TSH and a concomitant rise in the peak TSH response to TRH. The basal and peak levels of TSH were highly correlated (p less than 0.001). However, the iodide-induced rise in the peak TSH after TRH was poorly correlated with concomitant changes in serum thyroid hormones. Serum T3 wa not lower after iodide and, while serum T4 was somewhat lower, the fall in serum T4 was unexpectedly inversely rather than directly correlated with the rise in the peak TSH response to TRH. Thus, increased TSH secretion after iodide need not always be directly correlated with decreased concentrations of circulating thyroid hormones even when large doses of iodide are used. Clinically, a patient taking iodide may have an increased TSH response in a TRH stimulation test even though there is little or no change in the serum level of T3 or T4.