A. Eugene Pekary

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.

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.