Growth hormone (GH) secretion during nocturnal sleep and after clonidine in patients with essential hypertension

In order to estimate the neuroendocrine function of the central nervous system eventually leading to growth hormone (GH) secretion in essential hypertension, 17 patients with mild arterial hypertension (7 obese and 10 with normal body weight) were examined. The control group consisted of 16 normotensive volunteers (7 obese and 9 with normal body weight). The GH secretion was determined by radioimmunoassay during nocturnal sleep. In all the subjects, the serum GH was also measured after placebo and after the centrally acting alpha 2-adrenergic agonist-clonidine administered i.v. in a dose of 0.15 mg. The fasting serum insulin concentration was also measured in all the subjects. Clonidine decreased the mean arterial pressure in all the subjects investigated. However, in response to clonidine an increase in GH secretion in all hypertensive and normotensive cases with normal body weight was demonstrated, whereas in all obese hypertensive and normotensive patients no significant GH rise was found. It indicates that inhibition of GH secretion in patients with essential hypertension is related to coexistent obesity rather than with that of arterial hypertension. A strong (r = 0.76) and significant (p less than 0.0005) correlation demonstrated between the maximal GH concentration during the nocturnal sleep and after clonidine suggests that the mechanism of GH inhibition in response to both these stimuli is similar and it probably is related to the inhibition of neurohormonal secretion of the growth hormone releasing factor (GRF). However, the negative correlation between the fasting insulin concentration and GH response to clonidine shown in obese subjects only, points to a more complex mechanism of GH inhibition in obesity.