Previously we have reported that in the rabbit the sinus node impulse spreads not only to the atrial muscle but also to the musculature in the venae cavae proximal to the heart10, 19). On the basis of this result, Mashiba and coworkers have introduced into electrophysiology the concept of sinocaval conduction. Recently ARITA and coworkers reported on the mechanical activity of the vena caval muscle of the rabbito. Further studies on the sinocaval conduction of the rabbit have revealed that the transmission of the sinus node impulse to the superior venae cavae is delayed during passage through three different sites: one is the sinus node and the others are the junctions of right and left superior venae cavae with the right atrium. These junctional areas have been found to take over the function of impulse initiation under certain conditions. We have called them the sinocaval (SC) areas. The present paper mainly deals with the functional properties of the SC areas. METHODSThe experimental methods employed here were the same as described prey iouslylo. RESULTS

We have developed a new method for inducing portal hypertension and esophageal varices in rats--partial ligation of the portal vein after devascularization of the circumference of the left renal vein and complete ligation of the portal vein on the fifth day thereafter. Thirty rats were separated into groups of 10, control (sham operation), complete portal ligation only and complete portal ligation plus devascularization. Two weeks after the surgery, the presence of esophageal varices in rats with complete portal ligation plus devascularization was confirmed by portography and by the histological findings. The diameter (mean +/- SD) of the submucosal veins of the lower esophagus in the complete portal ligation plus devascularization group (219.4 +/- 86.6 microns) was significantly larger than that in the complete portal ligation group (99.8 +/- 53.4 microns) or in the control group (30.5 +/- 16.6 microns) (p less than 0.01). Vascular structures of the lower esophagus closely resembled those in humans with esophageal varices. This new technique is simple, rapid and reliable, and application can be made to various experimental studies on portal hypertension.

In recent years, it has become evident that the impulse originating in the sinus node spreads also to the right and left superior venae cavae proximal to the heart (sino-caval conduction), as well as to the atria ITO et al., 1963;ITO et al., 1964;YANAGA et al., 1966).In a previous paper (ARITA et al., 1966), spontaneous rhythmic contractions and action potentials were demonstrated in vitro rabbit, and the electrophysiological properties of the vena caval muscle have been studied comparing with those of the atrial muscle.Since some differences recognized between the venae cavae and atria in the electrophysiological properties (frequency-tension relationship, rest potentiation, cellular interconnection, etc.) seemed to include significant problems from the physiological and hemodynamic points of view, further investigations were undertaken.The present paper deals with the effects of epinephrine, norepinephrine, isoproterenol, propranolol, acetylcholine, atropine, ouabain, and their several combinations on the contractility and action potentials of the isolated left superior vena cava or inferior vena cava by using a strain gauge transducer and microelectrode technique. In several cases, the effects of these drugs on the isolated left atrium were also examined for comparison. METHODSThe proximal portion of the isolated left superior vena cava (LSVC) and the inferior vena cava (IVC), or the left atrium (LA) was prepared in essentially the

To determine whether the low density lipoprotein (LDL) receptor pathway is involved in the catabolism of plasma lipoprotein (a) [Lp(a)], serum lipids, Lp(a), and LDL receptor activity were measured in seven patients with hyperthyroidism before and after methimazole treatment given hyperthyroidism is associated with enhanced LDL receptor activity. LDL receptor activity in patients was estimated by the equation using the serum concentrations of apolipoprotein (apo) B and C-II. When euthyroidism was achieved after treatment, not only did serum total cholesterol, high density lipoprotein-cholesterol, apo B, and LDL-cholesterol (LDL-Ch) levels rise, but Lp(a) significantly increased and calculated LDL receptor activity significantly decreased. The changes in LDL receptor activity were significantly correlated with the changes in LDL-Ch as expected, but not with changes in Lp(a). These results suggest that the serum concentration of Lp(a) is lowered in hyperthyroidism, probably by a mechanism other than the enhanced activity of the LDL receptor, and that the LDL receptor pathway is involved in the catabolism of Lp(a) to a limited extent.

Since the pulsation of the vena cava was first noticed in the dog by Wallaenus in 1660 (FRANKLIN, 1937), the existence of rhythmical contractions of the venae cavae proximal to the heart in various animals has been reported