INFLUENCE OF GLUCOSE-LOAD ON CARDIOVASCULAR AND HUMORAL RESPONSES TO A COLD PRESSURE TEST

To investigate the relationship between insulin and reactivity to the cold pressure test four groups of mildly obese patients (12 per group: normotensive, essential hypertensive, normotensive (N-NIDD) and hyper tensive non-insulin-dependent diabetics (H-NIDD)) underwent a standard ised oral glucose tolerance test. During the test, BP and heart rate w ere monitored and venous blood samples were obtained at 0, 60 and 120 minutes to determine serum levels of glucose, insulin (mu U/ml), sodiu m, potassium (mEq/l), renin activity (ng/ml/hour), aldosterone, noradr enaline and adrenaline. The cold pressure tests were performed before glucose ingestion (I-CPT) and again at 60 minute after ingestion (II-C PT). As expected, glucose ingestion caused a significant increase in g lycaemia and serum insulin; the latter rose significantly more at 60 m inutes in normotensives (85+/-6) and essential hypertensives (83+/-5) than in N-NIDD (30+/-4) and H-NIDD (29+/-3). Plasma K significantly de creased in normotensives (4.4+/-0.1 vs. P<0.05) and essential hyperten sives (4.3+/-0.1 vs. 3.5+/-0.1, P<0.05) but did not change in either N -NIDD or H-NIDD. PRA significantly increased in normotensives (0.6+/-0 .1 vs. 1.2+/-0.1, P<0.01) and essential hypertensives (0.8+/-0.1 vs. 1 .5+/-0.2, P<0.05) but did not change in N-NIDD or H-NIDD. Plasma sodiu m and catecholamines did not change in any group. I-CPT induced simila r reactivity in all the groups. Mean BP (mmHg): normotensives + 22+/-5 , essential hypertensives + 21+/-6, N-NIDD + 19+/-5, H-NIDD + 22+/-5; heart rate (beats/min): normotensives + 4+/-1, essential hypertensives + 4+/-1, N-NIDD + 5+/-1, H-NIDD + 4+/-1. Plasma catecholamines rose s ignificantly and were similar in the four groups. On the contrary, aft er the II-CPT the mean BP reactivity was greater in normotensives (+ 3 5+/-6) and essential hypertensives (+ 31+/-5) than in N-NIDD and H-NID D, which was similar to that observed during the I-CPT. Plasma catecho lamines and heart rate were similar to those of the I-CPT in all the g roups investigated. On this basis we suggest a relationship between in sulin, the renin-angiotensin system and BP. Insulin increases reactivi ty to CPT and this action seems to be mediated by the renin-angiotensi n system. The effect of insulin on plasma potassium could be the link between insulin and the renin-angiotensin system.