Suppressing effects of short-chain fatty acids on growth hormone (GH)- releasing hormone-induced GH release in isolated anterior pituitary cells of goats

The involvement of tetrodotoxin-sensitive Na⁺ channels and receptor- operated nonspecific Ca²⁺ channels, and the effects of short-chain fatty acids, on growth hormone (GH) release induced by GH-releasing hormone (GHRH) were investigated in cultured and freshly isolated caprine anterior pituitary cells. In 3-d cultured cells in Dulbecco's modified Eagle's medium, an increase in GH release induced by GHRH (10 nmol/l) was moderately, but significantly, reduced by a voltage-sensitive Na⁺ channel antagonist tetrodotoxin (1 μmol/1). The GHRH-induced GH increase, which was not affected by a simultaneous addition of a receptor-operated nonspecific Ca²⁺ channel antagonist tetramethrine (0.1 mmol/1), was significantly reduced by a voltage-sensitive L-type Ca²⁺ channel antagonist nifedipine (1 μmol/l). Propionate and butyrate at 10 mmol/l, however, not only suppressed basal GH release but also significantly reduced the GH increase induced by 10 nmol/l of GHRH. The inhibitory action of these acids was also reproduced by an addition of β-hydroxy butyrate (10 mmol/l) and octanoate (10 mmol/l). In freshly isolated and perifused cells, butyrate (10 mmol/l) as well as somatostatin (100 nmol/l) significantly reduced the GH increase induced by GHRH. From these findings we conclude that tetrodotoxin-sensitive Na⁺ channels and voltage-dependent L-type Ca²⁺ channels are involved in the cellular mechanism for GHRH-induced GH release, and that short-chain fatty acids such as propionate and butyrate have a direct action on somatotrophs to reduce basal and GHRH-induced GH release, in caprine somatotrophs.