Effects of salsolinol and its antagonistic analogue, 1-MeDIQ, on growth hormone release in nursing sheep

Suckling induces a GH surge simultaneously to that of prolactin, so we tested whether salsolinol, a dopamine derivative (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline), participates in the regulatory process of GH secretion in lactating sheep. A series of intracerebroventricular (i.c.v.) infusions of salsolinol, in two doses, was performed in nursing sheep, without suckling, during the fifth week of lactation. In other suckling sheep, we infused i.c.v. a structural analogue of salsolinol – 1-methyl-3,4-dihydroisoqinoline (1-MeDIQ), which is able to antagonize salsolinol’s action. Intracerebroventricular treatment of nursing sheep with a lower dose of salsolinol (total 50 ng) significantly increased plasma GH concentration, as compared with the concentrations noted before the infusion and in nursing controls. A higher dose of salsolinol (total 5 μg) did not affect GH release significantly. Intracerebroventricular treatment with 1-MeDIQ (total 300 μg) significantly reduced basal GH release, not affecting a pattern of GH surge in response to suckling. In conclusion, salsolinol may affect the regulatory process of GH secretion in lactating sheep, but its role seems not to be major.