Detailed examination of episodic bursts of rGH secretion by high frequency blood sampling in normal male rats.
Episodic bursts of rat growth hormone (rGH) secretion were examined in detail by monitoring circulating rGH concentration every 2 min (70 ul blood samples were taken). Conscious free moving normal male rats implanted with indwelling cannulae were used. Between 11:00-13:00 h and between 14:00-15:20 h, basal levels of rGH were found to be 30-50 ng/ml. Bursts of rGH secretion had many different shapes, including a "single spike", "compound peak" and "plateau" but not regularity or periodicity of changes of rGH concentration was observed. Therefore we could not apply basic statistical treatments such as the standard deviation or standard error of means which are based on the assumption of normal distributions. When the downward slopes of each major spikes comprised more than 3 sequential samples, the decay slope was analyzed. Of 16 slopes, 10 were parallel with a theoretical curve of a 7 min half-life (rGH half-life is 5-7 min) indicating that no more rGH was secreted during the period of the downward slope. The slopes with significantly slower disappearance rates can be interpreted as indicating that a significant amount of rGH is secreted during the period of the downward slopes. Our experimental design revealed a more complex pattern or rGH secretory bursts than had hitherto been described. Our technique revealed more physiological characteristics of rGH secretion by more frequent sampling of very small volumes of blood. This technique eliminated unnecessarily excessive bleeding and avoided the necessity of returning red blood cells.
D000818:Animals; D001800:Blood Specimen Collection / Q000379:methods*; D013006:Growth Hormone / Q000378:metabolism*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D013006:Growth Hormone