Characterisation of the biological effects of neurohypophysial peptides on seminiferous tubules

Abstract

Oxytocin (OT) is present in the mammalian testis and has been postulated to play a role in modulation of seminiferous tubule contractility. However, recent evidence suggests that the myoid cells responsible for such contractile activity do not express OT receptors. In this study computer-assisted analysis and time-lapse videomicrography were used to investigate the biological effects of neurohypophysial peptides and their analogues on seminiferous tubule contractility. Adult rat testes were placed in fresh oxygenated Dulbecco's modified Eagle's medium (DMEM) F12 medium, decapsulated and the tubules gently teased apart. A small section of tubule was placed in a microslide chamber and perifused with medium. Seminiferous tubules were treated with OT (2 nM), [Arg8]-vasopressin (AVP, 0.2 nM) or [Thr4,Gly7]-OT (TGOT, 2 nM, 8 nM and 0.2 microM). Specific antagonists were also given simultaneously with OT and AVP treatments. Data were analysed to give arbitrary units of contractility. Both OT and AVP increased tubule contractility, with AVP being at least 10 times more potent than OT. Treatment with the selective OT antagonist, desGly-NH2,d(CH2)5[d-Tyr2,Thr4]-ornithine vasotocin (OTA, 0.2 microM and 2 microM) significantly reduced OT-induced increases in seminiferous tubule contractility but had no effect on AVP-induced responses. In contrast, the AVP antagonist, Phaa-d-Tyr(Me)-Phe-Gln-Asn-Arg-Pro-Arg-Tyr-NH2 (AVPA) was more potent at reducing AVP-induced increases than OT-induced responses. The selective non-peptide AVPA SR 49059 blocked the response to both peptides in a similar manner, whilst the non-peptide OTA L367,773 did not block OT-induced increases in seminiferous tubule contractility at doses that were slightly inhibitory to AVP-induced responses. The specific OT agonist TGOT did not induce a contractile response. The data in this study demonstrate that in the testis AVP acts via V1a receptors to stimulate contractile activity and suggest that OT may act via a receptor which differs from the classical V1a and uterine-type OT receptor. These findings support a role for OT in the regulation of seminiferous tubule contractility and raise the possibility that AVP may also be important in this process.

Oxytocin and Vasopressin Expression in the Ovine Testis and Epididymis: Changes with the Onset of Spermatogenesis1

“…In the marmoset, oxytocin immunoreactivity does not appear until spermatogenesis is underway, but the uterine-type oxytocin receptor is present before this in the juvenile [26], further illustrating the significant importance of the result presented here. However, changes in the density and regulation of an as-yet-uncharacterized receptor, as implicated in oxytocin-stimulated seminiferous tubule contractility [5], cannot be discounted.…”

“…Indeed, although the cauda epididymis does have considerable adrenergic innervation, disruption of the sympathetic supply from the mesenteric ganglion, while reducing its rate, does not abolish sperm transport [3]. The closely related neurohypophyseal peptides oxytocin and vasopressin have been implicated in stimulating contractile activity of the male reproductive tract, with each inducing dose-dependent seminiferous tubule contraction [4,5]. Oxytocin also increases contraction of the epididymis both in vitro [6] and in vivo [7], as do higher doses of vasopressin [7].…”

“…This suggests that both vasopressin and oxytocin may stimulate tubule contraction via the vasopressin receptor, and that vasopressin is the more important physiologically. However, studies us- ing specific agonists and antagonists of both peptides have revealed that the effects of oxytocin are probably mediated by a receptor that differs from the classical arginine vasopressin-V 1␣ and uterine oxytocin receptor [5]. Receptors for both peptides have been identified in the pig epididymis [28], but only the localization of oxytocin receptors to the epithelial and stromal tissue of the primate epididymis has been described [25,26].…”

Identification, localization and functional in vitro and in vivo activity of oxytocin receptor in the rat penis

“…Interestingly, the OTR gene is expressed in the penis in similar concentrations as those found in the prostate and testis, classically considered male targets for OT (Bathgate & Sernia 1994, Einspanier & Ivell 1997, Ivell et al 1997, Frayne & Nicholson 1995, Assinder et al 2000, Whittington et al 2001. In the latter tissues, OTR regulates steroidogenesis (Nicholson et al 1991, Nicholson & Jenkin 1995, Frayne & Nicholson 1995 and contractility (Bodanszky et al 1992, Frayne et al 1996, Harris & Nicholson 1998. In the penis, OTR is mainly localized in smooth muscle and regulates its in vitro contractile tone.…”

Regulation of 5α-Reductase Isoforms by Oxytocin in the Rat Ventral Prostate

“…In the testis (3,4) and epididymis (5), OT has been implicated in the regulation of contractility. OT has similar effects in both the human and rat prostate, producing an increase in prostatic tone and contractile activity (6).…”