Neonatal sympathectomy of normotensive Wistar-Kyoto and spontaneously hypertensive rats with 6-hydroxydopamine: effects on resistance vessel structure and sensitivity to calcium.

6-Hydroxydopamine (6-OHDA) was injected on alternate days from birth to 3 weeks of age into spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) control rats. The effects of this neonatal treatment on cardiovascular structure and mesenteric resistance vessel calcium sensitivity was studied in young (6 week) and adult (5 month) rats. Mean arterial pressure of treated SHRs and WKYs was reduced by 10% compared with control rats, but the heart:body weight ratio was unaffected by treatment. Both pharmacological and histological studies suggested that at 6 weeks of age, mesenteric resistance vessels from treated WKYs were completely denervated, but that vessels from treated SHRs still had sparse innervation. At 5 months all vessels from the treated rats had some adrenergic innervation, but less than the control rats. In the WKYs, treatment was associated with reduced media:lumen ratio and reduced calcium sensitivity of the mesenteric resistance vessels, while no such changes were observed in the SHR vessels. The results indicate that the sympathetic nervous system in SHRs is more resistant to chemical denervation than the sympathetic nervous system of the WKYs. The results also suggest that sympathetic innervation of mesenteric resistance vessels may affect vessel structure and sensitivity.