Preincubation with physiological concentrations of insulin affects contract
ile reactivity of isolated smooth muscle cells. We studied the effects of i
nsulin on intact aortic rings of Wistar rats preincubated 1-2 h with 240 pM
(I-1) and 960 pM (I-2) insulin with and without NO synthesis inhibition by
N-omega-nitro-L-arginine methyl ester (L-NAME). Resting force was tripled
by 0.1 mM L-NAME in control (C) and I-1 groups, but not in I-2 groups. I-1
treatment decreased the tachyphylaxis to two successive 1 mu M arginine vas
opressin (AVP) stimulations. Single contractions elicited by 1 mu M AVP, 1
mu M angiotensin II (AngII), or 0.01 mu M endothelin (ET1) were not affecte
d by insulin preincubation in either maximal force (F-max) or relaxation ti
mes. L-NAME enhanced F-max of AngII contractions by about 75% in C, 120% in
I-1, and 74% in I-2 groups; accordingly, it augmented the final steady-sta
te force in C and I-1 but not in It. Similarly, L-NAME increased F-max (30-
40%) of AVP and ET1 contractions in C and I-1 groups but failed to do so in
contractions of I-2 group. Results obtained with 10 mu M indomethacin sugg
est that this is due to insulin stimulation of prostacyclin effects.