The effects of aging and
hypertension on contraction were examined in rat mesenteric resistance arteries of 12- and 74-wk-old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). The vessels were suspended in myographs (37 degrees C, 95% O2-5% CO2) filled with modified Krebs-Ringer
bicarbonate solution. Isometric tension was measured. Contractions to KCl (100 mM) were similar in adult WKY and SHR; they increased in senescent WKY (P < 0.05) but decreased in senescent SHR (P < 0.05). Responses to
norepinephrine (% of KCl) were comparable in all four groups. However, blockade of
nitric oxide (NO) production with
NG-nitro-L-arginine methyl ester (
L-NAME) enhanced the sensitivity to
norepinephrine in senescent animals, particularly in SHR. Inhibition of
cyclooxygenase with
indomethacin prevented increased sensitivity to
norepinephrine after NO blockade. Responses to
angiotensin (ANG) II were not affected by aging and
hypertension, but the
thromboxane receptor antagonist
SQ-30741 reduced ANG II-induced contractions only in SHR of both ages (P < 0.05). Aging increased responses to ANG I in SHR but decreased it in WKY (P < 0.05). In quiescent rings with endothelium,
acetylcholine caused contractions in the presence of
L-NAME in adult and senescent SHR but not in WKY (P < 0.05).
SQ-30741 prevented these contractions (P < 0.05). Contractions to the
thromboxane analogue
U-46619 were reduced only in senescent SHR (P < 0.05). Thus aging increases and
hypertension decreases contractility of smooth muscle in rat mesenteric resistance arteries.(ABSTRACT TRUNCATED AT 250 WORDS)