Genome and hormones: Gender differences in physiology - Selected contribution: Sex differences in osmotic regulation of AVP and renal sodium handling

To determine sex differences in osmoregulation of arginine vasopressin (AV- P) and body water, we studied eight men (24 +/- 1 yr) and eight women (29 /- 2 yr) during 3% NaCl infusion [hypertonic saline infusion (HSI); 120 min , 0.1 ml.kg body wt(-1).min(-1)]. Subjects then drank 15 ml/kg body wt over 30 min followed by 60 min of rest. Women were studied in the early follicu lar (F; 16.1 +/- 2.8 pg/ml plasma 17 beta -estradiol and 0.6 +/- 0.1 ng/ml plasma progesterone) and midluteal (L; 80.6 +/- 11.4 pg/ml plasma 17 beta - estradiol and 12.7 +/- 0.7 ng/ml plasma progesterone) menstrual phases. Bas al plasma osmolality was higher in F (286 +/- 1 mosmol/kgH(2)O) and in men (289 +/- 1 mosmol/kgH(2)O) compared with L (280 +/- 1 mosmol/kgH(2)O, P < 0 .05). Neither menstrual phase nor gender affected basal plasma AVP concentr ation (P-[AVP]; 1.7 +/- 4, 1.9 +/- 0.4, and 2.2 +/- 0.5 pg/ml for F, L, and men, respectively). The plasma osmolality threshold for AVP release was lo west in L (x-intercept, 263 +/- 3 mosmol/kgH(2)O, P < 0.05) compared with F (273 +/- 2 mosmol/kgH(2)O) and men (270 +/- 4 mosmol/kgH(2)O) during HSI. Men had greater P-[AVP]-plasma osmolality slopes (i.e., sensitivity) compar ed with F and L (slopes = 0.14 +/- 0.04, 0.09 +/- 0.01, and 0.24 +/- 0.07 f or F, L, and men, respectively, P < 0.05). Despite similar Na+-regulating h ormone responses, men excreted less Na+ during HSI (0.7 +/- 0.1, 0.7 +/- 0. 1, and 0.5 +/- 0.1 meq/kg body wt for F, L, and men, respectively, P < 0.05 ). Furthermore, men had greater systolic blood pressure (119 +/- 5, 119 +/- 5, and 132 +/- 3 mmHg for F, L, and men, respectively, P < 0.05) than F an d L. Our data indicate greater sensitivity in P-[AVP] response to changes i n plasma osmolality as the primary difference between men and women during HSI. In men, this greater sensitivity was associated with an increase in sy stolic blood pressure and pulse pressure during HSI, most likely due to a s hift in the pressure-natriuresis curve.