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1 The effect of gamma-aminobutyric acid (GABA) on postganglionic sympathetic neurotransmission was studied in strips of the rabbit pulmonary artery. The strips were preincubated with 3H-noradrenaline and then superfused with 3H-amine-free medium. They were stimulated either electrically at 2 Hz, or by 60 mM potassium, or by 1 microM tyramine. 2 GABA (1 - 1000 microM) did not change the basal outflow of tritium, but decreased the electrically evoked overflow as well as the contractile response. GABA 1 microM decreased the evoked overflow by 12%, and GABA 1000 microM, by 42%. The effect of GABA was not changed by yohimbine, propranolol, cocaine, corticosterone, or indomethacin. It was not antagonized by picrotoxin or bicuculline methiodide. GABA 100 microM also slightly reduced the potassium-evoked overflow of tritium but did not change the tyramine-evoked overflow. 3 The results show that, in the pulmonary artery of the rabbit, GABA inhibits the release of noradrenaline. Its effect is independent of alpha- and beta-adrenoreceptors and is not mediated by prostaglandins. The effect may be due to activation of presynaptic receptors which appear to differ from conventional GABA receptors inasmuch as they are insensitive to blockade by either picrotoxin or bicuculline.

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The association of obesity and hypertestosteronaemia with elevated insulin concentration and dyslipidaemia was studied in 15 non-obese and 15 obese, hypertestosteronaemia patients; 14 non-obese and 10 obese, normotestosteronaemic subjects served as controls. Data were subjected to multivariate analysis. Enhanced body mass index (BMI kg/m2) resulted in a significant elevation of basal insulin (b-Ins), glucose-stimulated (delta) insulin (del-Ins), triglycerides (TG), very low density lipoprotein (VLDL), low density lipoprotein (LDL), and LDL/high density lipoprotein (HDL) ratio, and in a significant reduction of HDL. Furthermore, it was shown that BMI was positively correlated with TG, VLDL, LDL and LDH/HLD ratio, and negatively correlated with HDL in the normotestosteronaemic groups. Hypertestosteronaemia was associated with a significant increase of del-Ins, VLDL and LDL/HDL ratio, and with a significant decrease of HDL concentration. Testosterone was directly associated with del-Ins and LDL/HDL ratio, and inversely related to HDL in the non-obese groups. Summation effects of obesity and hypertestosteronaemia were found for del-Ins and VLDL. The data suggest that obesity and hypertestosteronaemia are independently and jointly associated with insulin resistance and dyslipidaemia, indicating an increased risk for coronary heart disease. The highest risk rate was found in obese hypertestosteronaemic patients. Serum testosterone may be a useful marker in detecting metabolic disorders connected with cardiovascular risk.