Reduction of Cold-Induced Hypertension by Antisense Oligodeoxynucleotides to Angiotensinogen mRNA and AT 1 -Receptor mRNA in Brain and Blood

Abstract

Abstract —Rats exposed chronically to mild cold (5°C/41°F) develop hypertension and cardiac hypertrophy. This provides a unique model of hypertension that is environmentally induced. The blood renin-angiotensin system (RAS) has been shown to play a role in both initiating and maintaining the high blood pressure (BP) in cold-induced hypertension. The mechanism also appears to involve both the tissue and brain RAS because there is increased mRNA for angiotensinogen (AGT) and angiotensin type 1 (AT 1 ) receptors in brain and peripheral tissues, an increased spontaneous drinking response, and an increased dipsogenic response to acute administration of angiotensin II (Ang II) in cold-treated rats. Antisense oligodeoxynucleotides (AS-ODN), targeted to the RAS, have been shown to reduce BP in spontaneously hypertensive rats. Therefore, we injected AS-ODN in rats with cold-induced hypertension to test whether antisense inhibition was effective in reducing this nongenetic nonsurgical hypertension. Sprague-Dawley rats were made hypertensive by cold exposure and injected intracerebroventricularly with AS-ODN to AGT mRNA (n=6) or AT 1 receptor mRNA (n=6). Systolic BP was recorded by tail cuff 24 hours later for 2 or 7 days, respectively. Systolic BP decreased significantly in response to AGT–AS-ODN (40±6 mm Hg, P <0.01) within 1 day after injection and to AT 1 receptor–AS-ODN ( P <0.05) for 3 days after injection. The maximum decrease was 41±10 mm Hg. Systolic BP then gradually increased to the preinjection level. The spontaneous drinking response to cold treatment also decreased significantly ( P <0.05) after AGT–AS-ODN or AT 1 receptor–AS-ODN intracerebroventricular injection. Intracardiac injection of AT 1 –AS-ODN (n=6) reduced systolic BP by 36±8 mm Hg ( P <0.05) and decreased AT 1 receptor as measured by autoradiography in aorta, adrenal glands, and kidneys 24 hours after injection. These data show that AS-ODN reduces BP in cold-induced hypertension and that the hypertension involves both peripheral tissues and central RAS in addition to blood-borne RAS mechanisms.