Steroid effects on the in vitro LH secretion from pituitary cells of sexually immature carp (Cyprinus carpio L.) under the influence of naltrexone and morphine

Dispersed cells from sexually immature carp (footlings) pituitaries were exposed to estradiol (E2) or testosterone (T) (both at 3 × 10 –8 M) in the presence of opioid receptor antagonist naltrexone (10–8 or 10–6 M) and/or agonist – morphine (10–8 or 10–6 M). Naltrexone alone at 10–6 M increased the LH level as compared with the control. Morphine (10–8 or 10–6 M), T and E2 had no influence on LH levels. The combination of T with naltrexone (10–8 M) stimulated LH release if compared with the control or with T alone. Morphine (both concentrations) with T caused significantly higher LH secretion than the control medium and T alone. Estradiol with naltrexone (10–8 and 10–6 M) had no influence on LH concentration. In media with E2 and morphine (10 –8 M) LH levels were higher than in the control and estradiol alone. The results show that in common carp sex steroids affect the response of pituitary cells to opioid agonist or antagonist giving an evidence on the role of steroids in LH release mediated by the opioid system.