HYPERTENSION INDUCED BY BRAIN GRAFTS FROM FETAL SPONTANEOUSLY HYPERTENSIVE RATS

Hypothalami from fetal rats were grafted into the third ventricle of f our strains of adult rats. Grafts from spontaneously hypertensive rats (SHR), in contrast to grafts from Wistar-Kyoto (WKY) rats, induced an elevation of systolic blood pressure and a thickening of the media of resistance arteries, along with corresponding alterations in the cont ractile properties of these vessels. However, no cardiac hypertrophy w as observed. The resistance arteries of rats grafted with hypothalami from SHR also displayed functional alterations that were similar to wh at is typically found in the resistance arteries of young prehypertens ive SHR, ie, an increase in the sensitivity to cocaine and an impairme nt in the ability to relax in the presence of acetylcholine. This sugg ests that the brain may play a causal role in these alterations. Histo logical examination of sections of brains grafted with previously labe led tissue revealed that (1) there was no brain area that was systemat ically infiltrated by grafts from SHR and not by grafts from WKY rats; (2) the volume of the transplants appeared larger 2 weeks after the g raft than the volume of the tissue originally implanted; and (3) graft s from SHR were slightly larger, displayed more individual foci, and e xtended farther along the anteroposterior axis than grafts from WKY ra ts. In addition, glial cultures derived from the hypothalami of SHR ha d a higher in vitro growth rate than equivalent cultures from WKY rats . It is therefore possible that the ability of brain grafts from SHR t o induce hypertension is related to a higher proliferative and/or migr atory potential of nonneuronal cells within the hypothalamus.