Previous investigations in this laboratory have shown the flexor carpi radialis muscle (FCR) of the cat to be compartmentalized with regard to the distribution of muscle fiber types. This study was undertaken to determine whether each compartment of the FCR had a distinct motor innervation band, or whether there was only one innervation band, as has been reported previously for other muscles. In order to assess variation in motor innervation banding patterns, the innervation bands were correlated with the muscle-tendon architecture. Each compartment of the FCR possessed a distinct innervation band. In addition, it was observed that the nerve to the FCR divided into a number of separate intramuscular branches which were distributed to the different histological compartments. It is possible that muscle fibers innervated by a single intramuscular nerve branch, and possessing a discrete innervation band, are locally organized within subdivisions of the FCR. It is hypothesized that the compartmental organization of the FCR would allow discrete regions of the muscle to function independently when performing different motor tasks.

The effects of angiotensin I (0.2-3.2 ju.g) and angioteasin II (0.1-1.6 fig) injections into the pump-perfused arterial supply of the liver were studied in dogs anesthetized with sodium pentobarbital. Marked increases in hepatic artery perfusion pressure (10-50%), reflecting directicnally similar changes in resistance to blood flow, were caused by either angiotensin I or angiotensin II. Resistance increases produced by angiotensin I were significantly attenuated by the synthetic nonapeptide SQ 20881 (Pyr-Trp-Pro-Arg-Pro-Gln-Iie-Pro-Pro, 50 j«,g/kg, iv) that inhibits enzymatic conversion of angiotensin I to ang:otensin II. In contrast; responses caused by angiotensin II were unaltered by SQ 20881. However, resistance increases caused by either angiotensin I or angiotensin II were blocked by 1-Sar-8-Ala-angiotensin II (100 /ug/kg mirr 1 , ia), a specific angiotensin II antagonist. These findings parallel the finding that responses to angiotensin I in the vasculature supplied by the hepatic artery are largely caused by local enzymatic conversion of angiotensin I to angiotensin II. Such conversion appears to occur to the extent of about 46$. importantly involved in local regulation of blood flow.We examined the effects of angiotensin I and angiotensin II on vascular resistance to blood flow in the vasculature supplied by the hepatic artery with and without a new inhibitor of the angiotensinconverting enzyme and with and without an angiotensin II antagonist. MethodsFourteen mongrel dogs of either sex (14-17 kg), anesthetized with sodium pentobarbital (30 mg/kg, iv), were intcbated with a cuffed endotracheal tube and permitted to breathe spontaneously. Systemic arterial blood pressure was measured with a catheter inserted into the right femoral artery and advanced into the thoracic cavity until its tip was close to the heart (Narco P-1000A pressure transducer).The left common carotid artery was exposed in the cervical region and carefully separated from the vagal nerve. A laparotomy was used to expose the hepatic artery. After all surgery was completed, heparin (500 units/kg, iv) was administered to prevent blood clotting. Blood from the left common carotid artery was diverted through a peristaltic Sigmamotor pump (T8) and used to perfuse the hepatic artery at a constant flow rate. Blood flow through the pump-perfused hepatic artery ranged between 70 and 90 ml/min in different dogs. In each experiment the pump was adjusted so that perfusion pressure was about 85% of systemi;: arterial blood pressure; preliminary studies

It has been demonstrated that there are significant differences in the ultrastructural morphology of the three mammalian myofiber types and their neuromuscular junctions (NMJ). The description of these ultrastructural differences was based primarily on samples taken from muscles that were composed of predominantly one fiber type. The objectives of this study were 1) to determine if previously described ultrastructural characteristics could distinguish between the three fiber types and the NMJ in a mixed muscle containing similar percentages of each fiber type and 2) to determine if there were significant differences in the morphology of like fiber types when compared between two histochemical regions in a muscle with a compartmentalized fiber-type distribution. The muscle used in this study was the flexor carpi radialis (FCR) of the cat. The objectives were achieved by a direct correlation of ultrastructure to histochemical profile on the same isolated myofibers. This study revealed a wide range of morpohological variation among fiber types in the FCR. Although many fibers from the FCR could be classified by using accepted ultrastructural criteria, most could not. Compartmental differences were present in several of the ultrastructural parameters measured. The slow-twitch oxidative (SO) and fast-twitch oxidative-glycolytic (FOG) fibers in the oxidative compartment had a significantly larger myofiber core volume when compared to the fast-twitch glycolytic (FG) fibers from both compartments. Also, the FG fibers in the glycolytic region had a significantly larger membrane volume (terminal cisternae, T tubules, and sarcoplasmic reticulum) when compared to the FOG fibers in the oxidative compartment and the SO fibers in both regions.This study has demonstrated that considerable variation exists in the most commonly accepted ultrastructural features used for distinguishing the three myofiber types when sampled from a mixed muscle that is not dominated by one fiber type. These results suggest the possibility of a greater functional range in the same type of histochemically identified motor units from mixed muscle than in those from muscles containing predominantly one fiber type.Classifications of mammalian myofiber types have used a variety of criteria to distinguish among fiber types (e.g., histochemical profile, physiological properties, and morphology; see reviews by Close, 1972;