Pituitaries were incubated in vitro for 5 hr and the quantity of GH released into the medium and remaining in the glands was bioassayed by the “tibia test.” Incubation was associated with a slight decline in the total GH in the system obtained by adding that released to that remaining in the pituitaries. There was considerable release of GH into the medium which amounted to 35% of the total GH in the system at the end of the incubation. The addition of GH-releasing factor (GRF) increased the release of GH and also increased the GH remaining in the glands by a factor of nearly 3 above the level of the controls incubated in the absence of extract in each of 6 experiments. These results indicate that GRF increases the synthesis as well as release of GH. An alternate explanation would be that GRF causes the activation of a precursor molecule to GH. GH-inhibiting factor (GIF) inhibited the release of GH as indicated by a decrease in the quantity released into the medium, but had no definite effect on that remaining in the glands. When GRF and GIF were both added, GIF blocked or partially blocked the effects of GRF on both release and apparent synthesis of GH. (Endocrinology85: 319, 1969)
No takes yet. Share an insight, caveat, or question.
Krulich et al. (1969) studied this question.