Introduction: Several observations have suggested that the secretion of neurohypophysial hormones could be modified by gonadotropin- releasing hormone (GnRH). Since, in medical practice, more often than GnRH itself, its analogues are used, the present study was undertaken to investigate the influence of the GnRH agonist — triptorelin on oxytocin (OT) and vasopressin (AVP) release from the rat hypothalamo-neurohypophysial (H-N) system both in vitro and in vivo.
Materials and methods: Male rats served as donors of the H-N explants, which were placed in 1 mL of Krebs-Ringer fluid (nKRF) and incubated successively in: 1 — nKRF (B1); 2 — incubation fluid as B1 enriched with an excess amount (56 mM) of K+ (S1); 3 — incubation fluid as B1 enriched with an appropriate concentration of triptorelin, i.e., 10^–11 — 10^–5 M (B2); and 4 — incubation fluid as S1 enriched with the same concentrations of triptorelin (S2). After 20 minutes of incubation, each medium (B1, S1, B2, S2) was collected and frozen before OT and AVP estimation by the RIA. During in vivo experiment, animals were infused intracerebroventricularly (icv) with triptorelin, at a concentration of 10^–7 M, and 20 minutes later they were decapitated. The neurohypophysis was dissected from the brain and blood plasma samples were collected and frozen for further OT and AVP RIA assays.
Results: The GnRH agonist — triptorelin stimulates both OT and AVP release from isolated H-N system at concentrations of 10^–9–10^–5 M. The strongest effect was displayed by triptorelin at a concentration of 10^–7 M. Under the conditions of K+ stimulation, triptorelin affects neither OT, nor AVP secretion in vitro. When infused icv, triptorelin, at a concentration of 10^–7 M, significantly stimulated both OT and AVP secretion into the blood.
Conclusions: Triptorelin may play a role as a neuromodulator contributing to the functional regulation of OT and AVP secretion in the rat.