Influence of age on the carotid bodies of spontaneously hypertensive (SHR) and normotensive rats. II. Alterations of the vascular wall.

The carotid bodies of spontaneously hypertensive rats (SHR) of the Okamoto-Aoki-strain and of age-matched normotensive Wistar rats (NWR) were studied with respect to their size and the histological appearance of their arterial vessels. The animals were aged 3-6 d, and 5-6, 15-20, 30-40 and 50-70 weeks. The development of hypertension in the SHR started at an age of 5-6 weeks and was fully established at 15-20 weeks (mean systemic arterial blood pressure at about 160 mm Hg). When compared with the age-matched normotensive control rats (NWR) the SHR in the established phase of hypertension showed enlarged carotid bodies, an increase of the thickness of the media of the carotid body artery and circumscript pad-like thickening of the vascular wall within the carotid bodies. Repeatedly in particular in the old SHR, also a hyalinosis of the small branches of the glomic artery was found. These pathological changes regularly narrowed the lumen of the vessels seized; sometimes to a considerable extent. Such vascular alterations were never found in the newborn (3-6 d old) SHR and were also not demonstrable in the NWR. Thus these vascular alterations in the carotid body vessels of the adult SHR are supposed to be the result of the high systemic arterial blood pressure. The data indicate that long-lasting high systemic arterial blood pressure leads to changes of the wall of the arterial vessels of the carotid and presumably also the aortic bodies thus inducing an ischemic hypoxia of the specific chemoreceptive tissue and a chronic stimulation of the arterial chemoreceptors.