The effect of stimulators and blockers of adrenergic receptors on LH secretion and cyclic nucleotide (cAMP and cGMP) production by porcine pituitary cells in vitro

The direct effects of alpha- and beta-adrenergic agents on luteinizing hormone (LH) secretion in vitro by porcine pituitary cells and the participation of secondary messengers, adenosine 3'5'-monophosphate (cAMP) and guanosine 3'5'-monophospate (cGMP), in transduction of signals induced by adrenergic agents and gonadotropin-releasing hormone (GnRH) in these cells have been investigated. Pituitary glands were obtained from mature gilts, which were ovariectomized (OVX) 1 month before slaughter, OVX gilts, assigned to four groups, were primed with: (1) vehicle (OVX); (2 and 3) estradiol benzoate (EB; 2.5 mg/100 kg b.w.) at 30-36 h (OVX + EB 1) or 60-66 It (OVX + EB 11) before slaughter, respectively; (4) progesterone (P-4; 120 mg/100 kg b.w.) for 5 consecutive days before slaughter (OVX + P-4). Anterior pituitaries were dispersed with trypsin and then pituitary cells were cultured (10 per well) in McCoy's 5a medium containing horse serum (10%) and fetal calf serum (2.5%) for 3 days, at 37degreesC and under the atmosphere of 95% air and 5% CO2. On day 4 of the culture, the cells were submitted to 3.5 h incubation in the presence of GnRH (a positive control), alpha- and beta-adrenergic agonists (phenylephrine (PHEN) and isoproterenol (ISOP), respectively), and alpha- and beta-adrenergic blockers (phentolamine (PHENT) and propranolol (PROP), respectively). The culture media were assayed for LH (experiment 1) and cyclic nucleotides (experiment 11). In experiment 1, addition of GnRH (100 ng/ml) increased LH secretion by pituitary cells taken from gilts of all experimental groups. The effects of alpha- and beta-adrenergic agents on LH secretion by the cells depended on hormonal status of gilts. The LH secretion by pituitary cells of OVX gilts was potentiated in the presence of PHEN (10, 100 nM, and 1 muM) and PHENT (1 muM), alone of in combination with PHEN (100 nM) and by the cells derived from OVX + EB I and OVX + P-4 animals in response to PREN (100 nM) and ISOP (1 muM). ISOP (1 muM) also stimulated LH secretion by the cells taken from OVX + EB II gilts. In experiment II, GnRH (100 ng/ml) increased cGMP production by pituitary cells obtained from all groups of gilts and cAMP secretion by the cells taken from OVX and OVX + P-4 animals. PHEN (100 nM) decreased and PROP (1 muM) enhanced cAMP production by pituitary cells derived from OVX + EB I and OVX gilts, respectively. Moreover, PHEN (100 nM) reduced, while PHENT (1 muM) stimulated the release of cGMP by pituitary cells taken from OVX + EB 11 animals. In turn, ISOP (100 nM) decreased and increased cGMP production by the cells derived from OVX + EB 11 and OVX + P-4 gilts, respectively. PROP (1 muM) potentiated cGMP accumulation by pituitary cells taken from OVX + EB I and OVX + P-4 animals. In conclusion, our results suggest that adrenergic agents can modulate LH release by porcine pituitary cells acting through guanyl and adenylyl cyclase and in a manner dependent on hormonal status of gilts. (C) 2002 Elsevier Science B.V. All rights reserved.