The effects of Clonidine on blood pressure, catecholamine and growth hormone release in hypogonadal men is preserved and not influenced by testosterone replacement therapy

It has been demonstrated that castration impairs the hypotensive effect of Clonidine in rat as well as its GH-releasing activity while testosterone replacement restores to normal the effects of alpha-2 adrenoceptor activation. Thus, these data point to main role of the gonadal steroid testosterone in modulating the effects of alpha-2 adrenergic activation on blood pressure, catecholamine and GH release in animal. Aim of the present study was to verify the activity of clonidine on blood pressure, catecholamine and GH release in human male hypogonadism before and after testosterone replacement. To this goal, 14 hypogonadal men (HP, age 33.8±2.9 yr; BMI < 25 kg/m2; 8 with hypergonadotropic and 6 with hypogonadotropic hypogonadism) received Clonidine administration (CLON, 300 μg po at 0 min) before and after 3 months of testosterone replacement (testosterone propionate depot, 250 mg i.m. every 21 days). Ten normal adult volunteers (NS, age 31.5±1.9 yr; BMI < 25 kg/m2) were studied as control group. In all subjects, before and after clonidine administration, systolic and diastolic blood pressure (SBP and DBP), pulse rate (PR), norepinephrine(NE), epinephrine (E) and GH levels were recorded. In HP basal testosterone levels were lower than those in NS (1.25 ± 0.3 vs 7.34 ± 1.5 ng/ml, p<0.05) and were restored to normal by hormonal replacement (6.91 ± 1.3 ng/mL) In HP, both SBP and DBP as well as PR were normal in basal conditions and were not modified by testosterone replacement. Both before and during testosterone CLON lowered SBP, DBP and PR in HP to the same extent observed in NS. In HP, basal NE levels were lower than those in NS (0.85 ± 0.15 vs 1.28±0.19 nmol/l, p<0.05) and were restored to normal during testosterone replacement (1.25 ±0.13 nmol/l). On the other hand, basal E levels in HP were similar to those in NS (179 ± 42 vs 197 ± 38 pmol/l) and were not modified by testosterone therapy (167±28 pmol/l). In HP, both before and during testosterone replacement, CLON reduced NE (0.44±0.10 and 0.58±0.07 nmol/l) levels to the same levels recorded in NS (0.68±0.08 nmol/l). Basal GH and IGF-I levels in HP (1.15±0.5 and 234±42 μg/l, respectively) were similar to those in NS (1.18±0.4 and 221±38 μg /I, respectively) and were not modified by testosterone (1.35 ± 0.6 and 256±32 μg/l, respectively). CLON administration induced a clear GH response in HP (F=37; p<0.001) which overlapped with that recorded in NS and was not modified by testosterone (F=1.7; P=NS). Our present findings demonstrate that, differently from in animal, in man testosterone has no role in modulating the effects of alpha-2 adrenergic activation by Clonidine on blood pressure, catecholamine and GH release. On the other hand, our data suggest the existence in male hypogonadism of a reduced basal noradrenergic activity which is restored by testosterone replacement.