Secretion of prolactin and growth hormone by teleost pituitariesin vitro

Summary

• 1. Anguilla pituitaries continue to synthesise and release both growth hormone (GH) and prolactin during long-term culture in high sodium medium (170 mM) and in low sodium medium (110 mM). Release of both hormones was greater in 110 mM than in 170 mM sodium and this difference was still apparent after 2 weeks culture for both total and newly synthesised hormones (Tables 1 and 3; Figs. 1 and 2).

• 2. Secretion of GH and prolactin was inhibited by high sodium medium after several days culture on 110 mM, but was not stimulated by low sodium medium after prior culture on 170 mM sodium (Tables 2 and 4).

• 3. Histologically, both GH and prolactin cells appeared more active and degranulated after long-term culture on 110 mM than on 170 mM sodium (Table 5; Fig. 3).

• 4. In isotonic medium, the release of GH byAnguilla pituitaries was inhibited by 1 μg/ml d l-thyroxine (Table 6).

• 5. Trout (Salmo gairdneri) pituitaries released GH and prolactin in steadily decreasing amounts on both low and high sodium media, while the pituitary concentrations fell to very low levels. There was no persistent difference in the rate of secretion on the two media during prolonged culture (Figs. 4 and 5).

• 6. During short-term incubations at 5 and 10° C high sodium inhibited GH release from trout pituitaries, but only the release of newly synthesised prolactin was inhibited (Tables 7 and 8).