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The reactivity to receptors and the Ca2+ availability in some vascular smooth muscles from SHRSP and WKY were investigated. (1) The affinity and the intrinsic activity (Ca2+ mobilization activity) to adrenaline receptor in femoral, mesenteric and renal arteries were not different between SHRSP and WKY. (2) The affinity to angiotensin receptor in thoracic aorta, portal vein and renal and mesenteric arteries is not different between SHRSP and WKY. But, the intrinsic activity to angiotensin receptor in thoracic aorta is decreased and that in mesenteric, renal arteries and portal vein is increased. (3) The reactivities to beta receptor and/or to C. AMP are increased in thoracic aorta and renal artery from SHRSP, while that in portal vein is decreased, being no change in femoral and mesenteric arteries. (4) The Ca2+ mobilization activity (Ca2+ influx and Ca2+ release) are accelerated in thoracic aorta and portal vein from SHRSP.

Because 2, 3DPG is one of the main factors which are concerned with the affinity of Hb for oxygen and 3PG is the degrading metabolite of 2, 3DPG, there are three following possibilities in SHRSP: 1) in pulmonary tissues the diffusion of oxygen may be interfered to some extent (cf. results 1 & 2), 2) in peripheral tissues the less releasing of oxygen from Hb may cause oxygen deficiency (cf. results 3 & 4) and therefore, these findings may be the underlying factors which cause hypertension (cf. result 6), and 3) the inability of producing 2, 3DPG may result in the decreased tolerance under oxygen deficiency, and the process of production or degradation of 2, 3DPG in SHRSP must have some defects.

When Ca uptake in the presence of ATP is referred to as (active plus passive) Ca transports and Ca uptake in the absence of ATP as passive one in microsomal fractions of SHRSP, there is an inverse effect between (active plus passive) Ca transports and passive transports. At 2 or 3 months old, when the hypertensive stage is remarkably progressing, the active Ca transport is lowered while passive one accelerated. Although this present result seems to be partly inconsistent with the Ca-ATPase activity, inverse relationship on Ca uptake in sarcoplasmic reticulum level is well agreement with the result of Ca effect on tonus of rat aortic strips. This observation on hypertensive development would be of interest in view that this Ca uptake rate has been lowered at 2 or 3 months old when hypertensive stage is progressing

Although it can be seen from above observations that (1) in male SHRSP, there were increasing activities of AT III with age reaching a peak on the age of high incidence of stroke, and (2) in female SHRSP, those of AT III were significantly higher compared with those of female WKY aged 3 to 9 months old, there were no marked difference in levels between male SHRSP and WKY. This leads us to conclude that there may be a certain correlation between higher values of AT III activity and the occurrence of stroke in its developmental course, but this high level of AT III may not be one of major factors for the stroke.In addition, in female both SHRSP and WKY, higher levels of AT III would be due to the chronic effect of estrogen.

Recently, Sasaki et al. have identified DPGM with DPGP (Eur. J. Biochem. 50, 581-593, 1975). This report and our results raised a possibility that in hypertension developmental state the enzyme activities of DPGM and DPGP in erythrocytes of SHRSP showed lower levels than those of WKY. And there is another possibility that in WKY these enzyme activities may be elevated by low partial pressure of O2 in enzyme inducing process, which was not observed in SHRSP. In addition, it is supposed that in WKY erythrocytes DPGM activity may be stimulated by Hb and inhibited by HbO2, whereas DPGP activity may be inhibited by Hb and stimulated by HbO2 in erythrocytes of WKY, which was not observed in SHRSP erythrocytes.

1) Effect of modified medium on tonus. The application of high concentration of Ca in medium produced an elevated tonus in SHRSP, but it did not so in WKR. This elevation in SHRSP was larger in 12M SHRSP than in 3M SHRSP. The authors reported that Ca influx was accelerated in SHRSP. These results agree with the previous report. The fact that the elevation of tonus was larger in 12M SHRSP than in 3M SHRSP suggests that the accelerated Ca influx may be more remarkable in 12M SHRSP than in 3M SHRSP. The elevation of tonus by a decrease of Na in medium was larger in SHRSP than in WKR. It was reported that the elevation of tonus by the decrease of Na might be due to Ca influx and Ca release. The fact that the elevation was found in younger SHRSP suggests that Ca influx and Ca release may be accelerated also in younger SHRSP. The fact that the elevation was larger in 12M SHRSP than in 3M SHRSP suggests that the accelerated Ca influx and Ca rlease may be more marked in 12M SHRSP than in 3M SHRSP. 2) Responses to K, NA and Ca. The responses to these contractile agents were larger in SHRSP than in WKR. The authors reported that the contractions by NA and K were due to Ca influx and Ca release. This result suggests that Ca influx and Ca release are more accel-erated in SHRSP compared with WKR. The fact that the contractions by these contractile agents were larger in 12M SHRSP than in 3M SHRSP suggests that the accelerated Ca influx and Ca release are more remarkable in 12M SHRSP than in 3M SHRSP. Immediately after the exchange to Ca-free medium, the contraction by NA was reduced in SHRSP, but that in WKR was not affected. This result suggests that the contraction by NA in SHRSP is due to Ca influx and Ca release, that in WKR being due to Ca release only. By a long time incubation in Ca-free medium, the contraction by NA disappeared in SHRSP and WKR. The disappearance time was shorter in SHRSP than in WKR. This suggests that the release of Ca from Ca store may be accelerated in SHRSP compared with WKR. The disappearance was also faster in 3M SHRSP than in 12M SHRSP. This fact suggests that the Ca content in store may be smaller in younger SHRSP than in older SHRSP