Biological studies with low and high molecular weight inhibin preparations

Serum and urinary prostatic inhibin-like peptide in benign prostatic hyperplasia and carcinoma of prostate

The levels of immunoreactive prostatic inhibin-like peptide (PIP), having follicle-stimulating hormone suppressing properties, were estimated in the sera and urine samples of patients with benign prostatic hyperplasia (BPH) and prostatic carcinoma (PC) as compared to age-matched controls. Significantly elevated serum PIP levels in BPH (107.8 +/- 19 ng/ml) and PC (88.7 +/- 9 ng/ml) patients were observed as compared to those in control men (10.2 +/- 1 ng/ml). Unlike serum, in urine high levels of PIP in BPH (294 +/- 49 micrograms/24 h) and extremely low levels in PC (23.6 +/- 5 micrograms/24 h) patients were seen as compared to control values (137.6 +/- 10 micrograms/24 h). Furthermore, striking differences were observed between the urinary PIP levels of BPH and PC patients. The results of the present investigation thus indicate the possible use of urinary PIP as a biological marker for prostate cancer.

Studies on low molecular weight follicle stimulating hormone receptor binding inhibitor (FSH-RBI) from ovine testis

Follicle stimulating hormone receptor binding inhibitor (FSH-RBI) has been isolated from the aqueous extracts of ovine testis using Sephadex column chromatography. Sephadex G-75 fraction IV was found to inhibit the binding of (125I) FSH to rat testis receptors. Further purification of Sephadex G-75 fraction on Sephadex G-25 column gave three fractions (I-III). The maximum inhibitory activity to inhibit (125I) FSH binding to rat testis receptor was associated with fraction III only. FSH-RBI exerted a greater inhibitory effect on the formation of the hormone-receptor complex rather than on the dissociation of the preformed complex. FSH-RBI did not inhibit the binding of (125I) LH to rat testis receptors. A significant decrease in the mouse ovarian weight was observed when FSH-RBI was injected to hCG-primed female mice. The molecular weight determination studies show that molecular weight of FSH-RBI is approximately 1400 Daltons.

Distribution of immunoreactive inhibin like material in different regions of human prostate

Distribution of immunoreactive inhibin material (IR-ILM) in different regions of human prostate was studied by using specific radio-immunoassay. Mean IR-ILM concentrations in the central, peripheral and periurethral zones were 27.3 +/- 9.3, 2.4 +/- 0.7 and 3.0 +/- 1.5 micrograms/mg protein respectively (P central vs periurethral and peripheral less than 0.05).

Stimulation of ornithine decarboxylase in the rat prostate by seminal plasma inhibin

The effect of seminal plasma inhibin on ornithine decarboxylase activity (ODC) in the rat prostate was studied. A single bolus injection of seminal plasma inhibin caused a 3- to 4-fold increase in ODC activity within 2 h whereas testicular ODC was unchanged. The ODC response to seminal plasma inhibin was neutralized by specific antibodies generated against the inhibin preparation. Another peptide, thyroid releasing hormone has no effect on prostatic ODC activity, but it blocked the increase in enzyme activity induced by treatment with seminal plasma inhibin.

Immunoreactive inhibin-like material in serum and gastric juice of patients with benign and malignant diseases of the stomach

Immunoreactive inhibin-like material (ILM) was measured by radioimmunoassay (RIA) in serum and gastric juice samples of 23 fasting normal men, 27 men with chronic superficial gastritis (CSG), and 21 men with carcinoma of stomach (5 for gastric analysis). Serum ILM levels in carcinoma of stomach patients (367 +/- 55.5 ng ml-1) were significantly higher than in normal men (15.4 +/- 2.6 ng ml-1; P less than 0.01) and in patients with CSG (109.8 +/- 17.7 ng ml-1; P less than 0.05). Sixty two per cent and 86% of patients with carcinoma of stomach showed elevated ILM levels which were higher than the highest noted in patients with CSG and normal men respectively.

Role of the prostate in the regulation of pituitary secretion of follicle stimulating hormone

The secretion of Follicle Stimulating Hormone by the pituitary gland is not regulated entirely by the negative feedback from gonadal steroids. There is ample evidence that the secretion of FSH is regulated by a non-steroidal hormone of gonadal origin termed "inhibin". Using a radioimmunoassay procedure, immunoreactive inhibin-like material was quantified in tissue and biological fluids to study its role in reproductive pathophysiology. High levels of immunoreactive inhibin were observed in human prostate as compared to testis. Biologically active as well as immunoreactive inhibin-like material (ILM) was obtained from human prostate, and was similar to that obtained from human seminal plasma under identical conditions. In patients with benign prostatic hypertrophy, high inhibin levels were observed which reduced after prostatectomy. The presence of immunoreactive inhibin in urine as well as semen of vasectomized and gonadectomized subjects indicates that prostate also secretes inhibin-like material. The specific receptors for inhibin as well as biosynthesis of inhibin in human prostate have been reported. Elevation of serum FSH levels following castration of adult male rats was further enhanced in animals where castration as well as prostatectomy was carried out. All these results demonstrate that apart from the testis, the prostate also secretes ILM and further suggest that the prostate along with testis, may play an important role in the regulation of pituitary secretion of FSH.

Levels of immunoreactive inhibin-like material in urine during the menstrual cycle

Using a specific and sensitive radioimmunoassay, the authors determined levels of inhibin-like material in the urine of eight healthy women with normal menstrual cycle length of 28 +/- 4 days. The results revealed a cyclic variation in urinary immunoreactive inhibin levels during the menstrual cycles, with a sharp rise in levels three to four days prior to luteinizing hormone (LH) and follicle-stimulating hormone (FSH) peaks. These levels of immunoreactive inhibin may thus serve as a parameter to detect impending LH surge.