Role of vasoconstrictors in the systemic hypertension of rats acclimatized to hypoxia.
Exposure to hypoxia (2-5 wk) results in systemic hypertension in rats and in humans. The possible mechanism(s) was investigated in rats acclimatized for 3 wk to barometric pressure of approximately 370 Torr (A) and in nonacclimatized littermates (NA) by administration of alpha-adrenergic [phentolamine (PHLM)], angiotensin II (ANG II), and arginine vasopressin (AVP V1) receptor antagonists. Both A and NA rats were studied in hypoxia (inspiratory O2 fraction = 0.10). Baseline mean arterial blood pressure (MABP) was higher in A than in NA rats: 126 +/- 4 vs. 101 +/- 2 mmHg (P < 0.05). Neither ANG II nor AVP V1 receptor antagonist influenced baseline MABP; however, both contributed to MABP recovery after PHLM. After simultaneous blockade of ANG II and AVP V1, PHLM lowered MABP by 65 +/- 2 and 45 +/- 3 mmHg in A and NA rats, respectively (P < 0.05). After combined blockade of the three systems, the smooth muscle relaxant sodium nitroprusside did not further modify MABP, which remained higher in A rats. It is concluded that 1) the hypertension in A rats is partly due to a higher alpha-adrenergic tone, 2) neither ANG II nor AVP contributes to the hypertension, but ANG II and AVP participate in MABP control after PHLM, 3) no other vasoconstrictor agents operate in either group, and 4) the higher MABP in A rats after sodium nitroprusside may reflect additional hypertensive mechanisms.
Moue
Y
Y
Department of Physiology, University of Kansas Medical Center, Kansas City 66160-7401, USA.
Smith
P G
PG
Clancy
R L
RL
Gonzalez
N C
NC
D000064:Acclimatization; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D006439:Hemodynamics / Q000187:drug effects; D006973:Hypertension / Q000150:complications / Q000188:drug therapy* / Q000503:physiopathology; D000860:Hypoxia / Q000150:complications / Q000188:drug therapy* / Q000503:physiopathology; D008297:Male; D010646:Phentolamine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D000317:Adrenergic alpha-Antagonists; D014662:Vasoconstrictor Agents; D000804:Angiotensin II; D010646:Phentolamine