Calcitonin inhibits testosterone and luteinizing hormone secretion through a mechanism involving an increase in camp production in rats

Abstract

Effects of calcitonin peptides, including human calcitonin (hCT), salmon calcitonin (sCT), and calcitonin gene-related peptide (CGRP), on the secretion of testosterone and luteinizing hormone (LH) in male rats were studied. Male rats were injected intravenously with human chorionic gonadotropin (hCG), calcitonin peptides, or hCG plus calcitonin peptides. Blood samples were collected at several intervals following hormone challenge. In an in vitro experiment, testis blocks were incubated with hCG (0, 0.05, 0.5, or 5 IU/ml) or hCG (0.5 IU/ml) plus calcitonin peptides (0-10(-9) or 10(-6) M) at 34 degrees C for 30 minutes. Both medium and plasma samples were extracted by ether and analyzed for testosterone by radioimmunoassay (RIA). The concentration of calcium in each plasma sample was measured by an automatic calcium analyzer. The anterior pituitary gland (AP) was incubated with or without calcitonin peptides (0-10 nM) at 37 degrees C for 30 minutes. They were then incubated with gonadotropin releasing hormone (GnRH, 10 nM) for a further 30 minutes. The concentration of LH in AP medium was measured by RIA. The accumulation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) in both testicular tissues and APs were measured by RIA. A single intravenous injection of calcitonin peptides decreased the basal and hCG-stimulated levels of plasma testosterone gradually from 60 to 180 or 360 minutes after challenge. The plasma calcium was not altered by the injection of calcitonin peptides and/or hCG. Administration of calcitonin peptides in vitro resulted in a dose-dependent inhibition of both basal and hCG-stimulated release of testosterone.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of catechin, epicatechin and epigallocatechin gallate on testosterone production in rat leydig cells

“…Male Sprague-Dawley rats weighing 300-350 g were housed in a temperature controlled room (22 AE 18C) with 14 h of artificial illumination daily (06:00-20:00 h) and given food and water ad libitum. Male rats, which were divided into 8 teams with 6-7 rats in each, were catheterized via the right jugular vein [Wang et al, 1994]. Twenty hours later, they were injected with saline (1 ml/kg) as vehicle, CCN (1 mg/ml/kg), EC (1 mg/ml/kg), EGCG (1 mg/ml/kg), human chorionic gonadotropin (hCG, 5 IU/ml/kg), hCG þ CCN, hCG þ EC, and hCG þ EGCG via the jugular catheter.…”

“…Plasma was separated by centrifugation at 8,000g for 3 min. The concentration of testosterone in each plasma sample was measured by radioimmunoassay (RIA) [Wang et al, 1994].…”

“…After incubation for 30 min with GTEs (10 À9 and 10 À5 M) in the presence or absence of gonadotropin releasing hormone (GnRH, 10 nM), the tissue was weighed and the medium was collected to measure the concentration of luteinizing hormone (LH) by RIA [Wang et al, 1994]. Preparation of rat testicular interstitial cells (TICs).…”

Calcitonin Functions Both as a Hypocalcemic Hormone and Stimulator of Steroid Production and Oocyte Maturation in Ovarian Follicles of Common Carp, Cyprinus carpio

“…We, therefore, suggest that signal for sCT-stimulated E 2 release might be transduced through cAMP pathway and interaction between sCT and hCG on the signal transduction in fish ovary is still open to elucidate. Increased production of cAMP caused by CT has been demonstrated in perfused rat bone, osteoblast like cell line, osteoclast, atria and aortic smooth muscle (Kubota et al, 1985;Sugimoto et al, 1986;Nicholson et al, 1987;Wang and Fiscus 1989;Iida-Klein 1992), and in rat testicular and anterior pituitary gland (Wang et al, 1994) substantiate the action of CT through cAMP path way in fish ovarian follicles. Our present finding on the stimulatory role of sCT on basal and hCG-induced E 2 production by fish ovarian follicles is completely opposite to the observed action of CT in mammalian ovary and testes in the regulation of steroid production.…”

“…Specific CT-binding sites have been found in brain and pituitary gland (Maurer et al, 1983) and in ovary and testis in mammal (Chausmer et al, 1982). Wang et al, (1994) found that www.intechopen.com CT-like peptides, human CT, salmon CT and CT-gene related peptide inhibit spontaneous and gonadotropin-stimulated testosterone secretion by acing directly on testes and also by reducing the release of pituitary luteinizing hormone (LH). Inhibition of salmon CT on secretion of progesterone-and gonadatropin-releasing hormone (GnRH)-stimulated release of pituitary LH in rat also has been documented (Tsai et al, 1999).…”