The TRH-like peptide pGlu-Glu-ProNH2 is present in the porcine pituitary but not in reproductive tissues

Characterization of a circulating N-extended form of the thyrotropin-releasing hormone-like peptide pGlu-Glu-Pro amide in human plasma

The TRH-like peptides pGlu-Glu-Pro amide, pGlu-Phe-Pro amide, and pGlu-Gln-Pro amide were isolated and identified some years ago, and these peptides have been proven to be present in many tissues and fluids. The presence of TRH-like immunoreactivity distinct from TRH in blood has been observed previously. In the present study, the presence of N-extended forms of TRH-like peptides in plasma has been investigated. Peripheral blood samples of human, rat, and rabbit were obtained and plasma was extracted. The peptides were separated in several steps of chromatography, including gel filtration, cation and anion exchange, and HPLC. The concentrations of the TRH-like peptides in the column fractions were measured by RIA with TRH antibody. The N-extended forms of TRH-like peptides were determined by RIA after trypsin digestion. In human plasma it was observed an N-extended form of TRH-like peptides in substantial concentration. After trypsin and heating, the N-extended forms of TRH-like peptides were rechromatographed on Sephadex G-50. This showed that the TRH-like peptides released have a similar size to TRH. The peptides were then separated by cation exchange chromatography, and the major fraction was unretained, indicating a neutral or acidic nature. Part of the unretained fraction was then chromatographed on anion exchange column in which the major fraction was retained, demonstrating the acidic nature of the peptides. Similar results have been observed in rat and rabbit. The other part of the unretained fraction from cation exchange chromatography of human plasma was purified on HPLC. The results demonstrated that the major component observed by HPLC cochromatographed with synthetic pGlu-Glu-Pro amide. This study represents the first demonstration of a circulating N-extended form of any TRH-like peptide.

Modulation of the function of boar spermatozoa via adenosine and fertilization promoting peptide receptors reduce the incidence of polyspermic penetration into porcine oocytes

Effects of adenosine and pGlu-Glu-ProNH(2) (FPP) on the function and in vitro penetration of boar spermatozoa were examined. First, the effects of dibutyryl cAMP or agonists and antagonists of adenosine receptors (inhibitory adenosine receptors, A1AdR; stimulatory adenosine receptors, A2AdR) on freshly ejaculated spermatozoa were determined by chlortetracycline fluorescence assessment. Capacitation of spermatozoa was stimulated when they were cultured in a medium with dibutyryl cAMP, adenosine, A2AdR agonist, and adenosine plus A1AdR antagonist (CPT). However, acrosome reaction was inhibited only by adenosine. A1AdR agonist did not affect intact spermatozoa. A2AdR antagonist (DMPX) neutralized all of the effects of adenosine. Second, interaction of adenosine and FPP was examined. Gln-FPP, a competitive inhibitor of FPP, and DMPX inhibited the effects of adenosine and FPP, and CPT neutralized the inhibitory effect of FPP on acrosome reaction. Last, the effects of adenosine, FPP, and caffeine on the rate of sperm penetration were examined using frozen-thawed spermatozoa. Adenosine, FPP, and caffeine significantly enhanced the rate of sperm penetration as compared with the case of no additions. Caffeine treatment resulted in a high rate of polyspermic fertilization. In contrast, adenosine and FPP treatments resulted in an increased proportion of normal fertilization in in vitro-matured oocytes. These results suggest that boar spermatozoa can be modulated by the adenylyl cyclase/cAMP pathway via A2AdR in intact cells to induce capacitation and A1AdR in capacitated cells to inhibit spontaneous acrosome loss and that FPP receptors interact with A2AdR in intact cells and with A1AdR in capacitated cells. Furthermore, adenosine and FPP seem to be useful in reducing the incidence of polyspermic penetration.

Characterization of neutral TRH-like peptides in mammary gland, mammary tumors and milk

Three pyroglutamylpeptide amides, pGlu-Glu-Pro amide, pGlu-Phe-Pro amide and pGlu-Gln-Pro amide, with similar structures to thyrotropin-releasing hormone (TRH), have been identified previously in the male reproductive system. We report here that rat and human mammary gland contain neutral TRH-immunoreactive peptides which are not retained on cation or anion exchange chromatography and that similar peptides occur in the milk of rat, cow, ewe and sow. The TRH-like peptides in lyophilized milk from the cow were purified by gel exclusion chromatography, mini-column cation exchange chromatography and reversed phase high performance liquid chromatography (HPLC) and the chromatographed peptides were located by TRH radioimmunoassay (RIA). In each chromatographic system the major TRH-immunoreactive peptide from cow milk exhibited identical behavior to pGlu-Phe-Pro amide; in addition there were two minor TRH-immunoreactive components. The possible physiological role of the TRH-like peptides in the mammary gland is discussed. In a series of patients with breast carcinoma, mammary tumor tissue was shown to contain approximately four times more TRH-like peptide than normal mammary tissue from the same patient, raising the possibility that the TRH-like peptides may be implicated in tumor development.

Both fertilization promoting peptide and adenosine stimulate capacitation but inhibit spontaneous acrosome loss in ejaculated boar spermatozoa in vitro

Both fertilization promoting peptide (FPP) and adenosine stimulate capacitation and inhibit spontaneous acrosome loss in epididymal mouse spermatozoa; these responses involve modulation of the adenylyl cyclase (AC)/cAMP signal transduction pathway. However, it was unclear whether these responses were restricted to the mouse or possibly common to many mammalian species. To address this question, the response of boar spermatozoa to FPP and/or adenosine was evaluated. FPP is found in nanomolar concentrations in seminal plasma of several mammals, but not the pig. When cultured in caffeine-containing Medium 199 for 2 hr, chlortetracycline fluorescence evaluation indicated that neither FPP nor adenosine stimulated boar sperm capacitation per se but did inhibit spontaneous acrosome loss. However, in caffeine-free medium, FPP and adenosine both stimulated capacitation and inhibited spontaneous acrosome loss, suggesting that boar spermatozoa have receptors for both FPP and adenosine. Gln-FPP, a competitive inhibitor of FPP in mouse spermatozoa, has recently been shown to inhibit mouse sperm responses to adenosine as well, suggesting that FPP receptors and adenosine receptors interact in some way. Used with boar spermatozoa, Gln-FPP also significantly inhibited responses to both FPP and adenosine. These responses suggest that mechanisms whereby FPP and adenosine can regulate sperm function, via AC/cAMP, are of considerable physiological significance. Mouse, human, and now boar spermatozoa have been shown to respond to FPP, suggesting that these mechanisms may be common to many mammalian species. We also suggest that the effects of FPP and adenosine could also be exploited to maximize monospermic fertilization in porcine in vitro fertilization.

Identification of the TRH-like peptides pGlu-Glu-Pro amide and pGlu-Phe-Pro amide in rat thyroid: regulation by thyroid status

Rat thyroid contains thyrotropin-releasing hormone (TRH) and TRH-like peptides which react with TRH antisera. We have identified the TRH-like peptides in the thyroid and examined whether their levels are influenced by thyroid status. The peptides were extracted from the thyroid glands of five hyperthyroid rats and purified by ion-exchange chromatography on SP-Sephadex C25 and reversed-phase high performance liquid chromatography. The principal TRH-immunoreactive component exhibited the same retention on HPLC as synthetic pGlu-Glu-Pro amide and a secondary component corresponded to synthetic pGlu-Phe-Pro amide. In agreement with these assignments the main peptide was shown to be acidic when chromatographed on DEAE-Sephadex A25 and the second peptide neutral. The levels of TRH and TRH-like peptides in the thyroid were investigated in hyper-, hypo- and euthyroid rats. Hyperthyroidism was induced by chronic subcutaneous administration of triiodothyronine (T3) and hypothyroidism was produced by addition of propylthiouracil (PTU) to the drinking water. The amounts of the peptides were determined by radioimmunoassay with a TRH-antiserum, carried out after extraction from the tissues and purification by ion exchange chromatography. The mean concentration of TRH-like peptides in the thyroids of the hyperthyroid rats was 95.5+/-25.5 pmol/g, the mean concentration in the hypothyroid rats was 11.7+/-3.4 pmol/g, and in the euthyroid rats 17.6+/-3.2 pmol/g. The concentrations of TRH were less influenced by thyroid status: the values in hyper-, hypo- and euthyroid rats were 47.5+/-9.4, 42.1+/-6.3, and 17.2+/-1.6 pmol/g respectively. The results show that the levels of the TRH-like peptides in rat thyroid are highly sensitive to thyroid status, suggesting a possible involvement in thyroid regulation.

The thyrotropin-releasing hormone-like peptides pGlu-Phe-Pro amide and pGlu-Glu-Pro amide increase plasma triiodothyronine levels in the mouse; the activity is sensitive to testosterone

Three naturally occurring peptides, pGlu-Glu-Pro amide, pGlu-Phe-Pro amide and pGlu-Gln-Pro amide, with similar structures to thyrotropin releasing hormone (TRH) have recently been identified but no studies of their in vivo activities have been reported previously. We describe here the ability of pGlu-Phe-Pro amide and pGlu-Glu-Pro amide to influence thyroid status. Subcutaneous administration of these 'TRH-like' peptides in male and female CDI mice led to increased levels of triiodothyronine (T3) and to a lesser extent tetraiodothyronine (T4) in the circulation. pGlu-Phe-Pro amide was more potent than pGlu-Glu-Pro amide; it exhibited a similar potency to pGlu-His-Pro amide (TRH). pGlu-Phe-Pro amide, pGlu-Glu-Pro amide and TRH produced significantly greater effects in the female than in the male. Castration of male mice led to increased activities, with potencies comparable to those seen in the female; in contrast treatment of female mice with testosterone resulted in reduced activities, similar to those observed in the control male. The effects of potassium deprivation on the activities of the TRH-like peptides were also investigated. This diet, which results in decreased testosterone levels in the male, led to increased activities of the TRH-like peptides and TRH, approaching the potencies observed in the female. The results demonstrate that the TRH-like peptides pGlu-Phe-Pro amide and pGlu-Glu-Pro amide which occur naturally in the thyroid gland exhibit biological activity in influencing thyroid status in vivo. The activities are sensitive to testosterone.

Fertilization-promoting peptide in reproductive tissues and semen of the male marmoset (Callithrix jacchus)

Fertilization-promoting peptide (FPP) is present in the prostate gland and semen of some mammals, and has been shown to enhance the fertilizing ability of both epididymal mouse and ejaculated human spermatozoa. The novel peptide may prove of importance for the treatment of some cases of male infertility, and a suitable animal model would be useful to test this hypothesis. To this end, we examined reproductive tissues and semen of the male marmoset for the presence of FPP. Peptides were extracted from seminal plasma, testes, prostate, and bulbourethral glands of intact and castrated male marmosets. The peptides were identified by ion-exchange chromatography followed by radioimmunoassay. The mean concentration of FPP immunoreactivity in semen from intact males was 58.7 nM (SE +/- 9.9 nM, n = 10), and anion-exchange chromatography revealed FPP as the only immunoreactive peptide present. Analysis of tissues revealed that FPP in semen was likely to be derived from the prostate gland, which contained this peptide as the major source of immunoreactivity (10.86 pmol/gland; SE +/- 4.39 pmol/gland, n = 4). Only low concentrations of FPP were detectable in the bulbourethral glands, and the peptide was undetectable in the testis. Surprisingly, FPP was readily detectable in the seminal plasma from one castrated marmoset and was present in the prostate gland from 3 castrates at levels which did not differ significantly from those in intact animals (5.47 pmol/gland, SE +/- 1.64 pmol/gland, n = 3). Plasma testosterone measurements indicated that residual circulatory androgens remained after castration, which may be consistent both with the maintenance of mating behavior and the presence of prostatic FPP. We conclude that FPP is present within the prostate gland and seminal plasma of the marmoset at concentrations consistent with a role in male fertility in this species.

Peptides related to thyrotrophin-releasing hormone (TRH) in human prostate and semen

The TRH-related peptide, pGlu-Glu-ProNH2, which was first identified in rabbit prostate has recently been named fertilization-promoting peptide (FPP) because of its ability to enhance the in vitro fertilizing potential of mouse epididymal spermatozoa. This study set out to examine the nature of the TRH-related peptides in human prostate and semen but, first, the optimal conditions for collection of semen samples were investigated. FPP was degraded slowly (t1/2 = 163 min, S.E. +/- 51.3, n = 6) in seminal plasma which has allowed us to measure accurately the concentrations of FPP, after extraction of the peptide in acidified acetone precisely 5 min after ejaculation. In this way, high levels of FPP (mean: 49.5 nmol/l) were detected in normal human semen, from young men, although other TRH-related peptides did not appear to be present. We have also examined the TRH-related peptides present in prostate samples from clinical patients both with and without evidence of benign prostatic hyperplasia (BPH), by ion-exchange chromatography followed by radioimmunoassay. Substantial concentrations of FPP were observed in normal (4.10 pmol/g tissue, S.E. +/- 1.46) and BPH prostate (6.27 pmol/g tissue, S.E. +/- 1.65). In addition, a second, neutral TRH-immunoreactive peptide was always detected in BPH tissue (7.40 pmol/g tissue, S.E. +/- 1.98) with only low levels generally present in normal prostate. The possibility that the presence of high levels of the neutral peptide in prostate may be used as an indicator of the onset of BPH deserves further scrutiny.

Stimulating effect of pyroglutamylglutamylprolineamide, a prostatic, TRH-related tripeptide, on mouse sperm capacitation and fertilizing ability in vitro

Pyroglutamylglutamylprolineamide, a prostatic tripeptide with structural similarities to thyrotrophin-releasing hormone (TRH), has been found in the seminal plasma of several mammalian species, suggestive of a biological function relating to spermatozoa. Using chlortetracycline (CTC) fluorescence analysis and in vitro fertilization, we have obtained evidence that the tripeptide stimulates mouse sperm capacitation and fertilizing ability in vitro. The tripeptide at concentrations from 5-500 nM was added to sperm suspensions and cells were assessed with CTC after 40 min, insufficient time for complete capacitation by a majority of spermatozoa under standard conditions of incubation. Concentrations of 25 nM and higher significantly promoted capacitation, as evidenced by a decrease in the proportion of acrosome-intact F pattern spermatozoa, characteristic of uncapacitated cells, and an increase in the proportion of acrosome-intact B pattern spermatozoa, characteristic of uncapacitated cells. However, there was no significant stimulation of acrosomal exocytosis. These results suggested that peptide-treated cells would be more fertile than their untreated counterparts. This was confirmed using in vitro fertilization, where the presence of 100 nM peptide during sperm preincubation and gamete coincubation significantly stimulated fertilizing ability (peptide, 56.5% of oocytes fertilized; controls, 26.5%). Comparison of the prostatic tripeptide and TRH effects on capacitation revealed that TRH at a concentration of 250 nM was as effective as the prostatic tripeptide in promoting the F-->B transition but was less effective or ineffective at lower concentrations. In vitro fertilization assessment of the two peptides, at 100 nM, revealed that only the prostatic tripeptide significantly stimulated fertility. Again, this was consistent with the CTC analyses.(ABSTRACT TRUNCATED AT 250 WORDS)