Humoral factors trophic for vascular smooth muscle during the development of hypertension in rats.

There is evidence that a humoral factor or factors in rats with one-kidney, one-clip (1K1C) hypertension increase growth of cultured vascular smooth muscle cells. Such humoral trophic factors may contribute to the abnormal growth of arterial muscle in hypertension. To further study the longitudinal expression of this trophic factor or factors, we prepared rats with 1K1C hypertension of different durations. To determine if the factor or factors are also expressed in other forms of experimental hypertension, we additionally prepared rats with two-kidney, one-clip (2K1C) hypertension and paired two-kidney (2K) normotensive controls; we also studied Spontaneously Hypertensive Rats (SHR) plus appropriate controls. In the presence of growth stimulated by background levels (1%) of fetal calf serum, 20% platelet-poor, plasma-derived serum (PDS) from 1K1C rats 8-14 days (n = 10) and 28 days (n = 12) after clipping increased [3H]-thymidine incorporation of growth-arrested cultured rat aortic smooth muscle cells more than the paired 1K PDS, by up to +67% and +40%, respectively (P < 0.01). However, with PDS from 1K1C rats 4 days (n = 11) and 38 days (n = 6) after clipping there was no evidence for a differential effect (P > 0.5 and P > 0.1, respectively). PDS from seven 2K1C rats (at 9 days) also increased [3H]-thymidine incorporation of the assay cells more than PDS from the paired 2K rats, by up to +19% (P < 0.05). However, there was no evidence that PDS from SHR differentially increased cellular thymidine incorporation. Thus, evidence from this study suggests that the humoral factor or factors trophic for vascular smooth muscle are expressed in both low- and high-renin forms of experimental renovascular hypertension, but not in the very early or in the late complicated stages of the hypertension, or in genetic hypertension in rats.