Stress- as well as suckling-induced prolactin release is blocked by a structural analogue of the putative hypophysiotrophic prolactin-releasing factor, salsolinol.

Prolactin is secreted from the anterior lobe of the pituitary gland in response both to suckling and to stress. We recently observed that 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), produced in the neurointermediate lobe of the pituitary gland, as well as in the medial basal hypothalamus, can selectively release prolactin from the anterior pituitary. Therefore, it has been proposed that salsolinol is a putative endogenous prolactin-releasing factor (PRF). Here, we report that one structural analogue of salsolinol, 1-methyl-3,4-dihydroisoquinoline (1MeDIQ), can block salsolinol-induced release of prolactin, but does not affect prolactin release in response to thyrotropin releasing hormone (TRH), alpha-methyl-p-tyrosine (alpha MpT) (an inhibitor of tyrosine hydroxylase), domperidone (a D(2) dopamine receptor antagonist), or 5-hydroxytryptophan (5-HTP), a precursor of serotonin). 1MeDIQ profoundly inhibited suckling-, immobilization-, as well as formalin-stress induced prolactin release without any influence on corticosterone secretion. The 1MeDIQ-induced reduction in prolactin response to immobilization stress was dose-dependent. These results suggest that salsolinol can play a pivotal role in the regulation of prolactin release induced by either physiological (suckling) or environmental (stress) stimuli.

Comparison of 3H-thymidine incorporation and CellTiter 96 aqueous colorimetric assays in cell proliferation of bovine mononuclear cells.

A rapid colorimetric non-radioactive assay for the determination of bovine mitogen-induced lymphocyte proliferation in cell culture was evaluated using a novel tetrazolium compound (MTS) and an electron coupling reagent (PMS) provided in the CellTiter 96 kit (Promega). The results of the new method were compared with those of the 3H-thymidine incorporation assay using parallels obtained from the same lymphocyte population. The concentrations used in the cell suspension of primary cultured lymphocytes resulted in a significant signal/background ratio when cells were prepared from peripheral blood, spleen or mesenteric lymph nodes. The same concentrations of thymocytes resulted in a weak signal even for the highest concentrations of mitogen. A good correlation was demonstrated between the results of the two methods. The non-radioactive method performed well in assays in bovine mononuclear cells derived from prolactin-treated or -untreated calves, showing a 50% lower responsiveness to mitogenic stimulation in prolactin-deprived animals.