ANTIHYPERTENSIVE EFFECT OF THYMECTOMY IN LYON HYPERTENSIVE RATS - VASCULAR REACTIVITY, RENAL HISTOLOGY, AND SODIUM-EXCRETION

The aim of this study was to search for the possible mechanisms involv ed in the antihypertensive effect of neonatal thymectomy that we previ ously observed in Lyon hypertensive (LH) rats. To that end, we studied in LH and normotensive control(LN) rats the consequences of neonatal thymectomy on vascular reactivity, renal structure, and pressure-natri uresis. The increase in presser responses to angiotensin I and phenyle phrine noted in LH rats as compared to LN animals was abolished by neo natal thymectomy. Histological study showed that kidneys from LH rats exhibited arterial wall hypertrophy, segmental hyalinization of the gl omeruli, and were infiltrated by mononuclear cells. All these features of kidney injury were reduced in neonatally thymectomized LH rats. La stly, the responses of isolated perfused kidneys from LH rats to stepw ise reductions in renal perfusion pressure differed from those of LN r ats by decreased renal perfusion flow and natriuresis. Neonatal thymec tomy tended to improve sodium excretion in parallel with a slight decr ease in renal vascular resistances. It is concluded that the normaliza tion of vascular responsiveness to vasoconstrictor factors, the allevi ation of renal lesions and, to a lesser extent, the moderate improveme nt of pressure natriuresis may account, at least in part, for the anti hypertensive effect of neonatal thymectomy in LH rats.