Tissue distribution of cholesterol feedback control in the guinea pig.

The level of cholesterol synthesis and the activity of the cholesterol feedback system were studied in tissue slices from a number of organs of the guinea pig. In contrast to the tissue distribution of sterol synthesis in the rat, liver slices of the guinea pig have a low rate of sterologenesis, with ileum and lung being the most active sterologenic tissues. More surprising, all tissues studied in the guinea pig, including lung, ileum, and brain, were shown to possess an active cholesterol feedback system. The basis for the widespread organ distribution of cholesterol feedback control in the guinea pig is probably the ability of the various tissues of the guinea pig to take up and concentrate exogenous cholesterol and is not the result of any inherent differences in the lipoprotein composition in this species.     

GTP hydrolysis by guinea pig liver transglutaminase

Homogeneous guinea pig liver transglutaminase was purified from a commercially available enzyme preparation by affinity chromatography on GTP-agarose. The purified transglutaminase exhibited a single band of apparent Mr = 80,000 on sodium dodecyl sulfate polyacrylamide gel and Western blotting and had enzyme activity of both transglutaminase and GTPase. The guinea pig liver transglutaminase has an apparent Km value of 4.4 microM for GTPase activity. GTPase activity was inhibited by guanine nucleotides in order GTP-gamma-S greater than GDP, but not by GMP. These results demonstrate that purified guinea pig liver transglutaminase catalyzes GTP hydrolysis.     

Effects of guinea pig vasoactive intestinal peptide on the isolated perfused guinea pig heart

The pharmacological effects of guinea pig vasoactive intestinal peptide (VIP) were studied in isolated perfused guinea pig hearts. Bolus injections of VIP produced a dose-dependent tachycardia that was not affected by atenolol. A decrease in amplitude of ventricular contractions occurred in response to all doses of VIP. This response was preceded by a small increase in amplitude in 3 of 6 hearts at the highest dose. VIP produced a decrease in perfusion pressure which was prominent after coronary tone was elevated with [Arg8]-vasopressin. The present findings support speculation that VIP may have a role in the regulation of heart rate and coronary blood flow.     

Contraction of guinea pig uterus by synthetic leukotrienes

Synthetic leukotrienes (LT) C₄ and D₄ elicited concentration-dependent contractions of the guinea pig uterus between 10^?8-10^?6M, whereas LTE₄ appeared 1000-fold weaker. The potencies of LTC₄ and LTD₄ were similar to that of acetylcholine and PGF_2α but weaker than that of PGE₂. The maximal contractions elicited by LTC₄ and LTD₄ were 66.0 ± 2.1% and 63.8 ± 4.6% that elicited by acetylcholine. FPL 55712 (10^?5M) antagonized the uterine contractile activity of LTD₄, while meclofenamic acid at 10^?5M but not at 10^?6M also antagonized the LTD₄-induced contration. Radioimmunoassay of the uterine tissue bathing fluid following LTD₄ indicated the variable presence of low concentrations of PGE₂, PGF_2α and TXB₂. These results demonstrate the LTC₄ and LTD₄ possess significant uterine contractile activity, which may only partially be mediated indirectly via prostaglandin products.     

Potentiation of the cGMP-induced guinea pig acrosome reaction by zinc

The addition of 8 bromo cGMP (10 mM) immediately (approximately 2 min) upon suspension of Guinea pig sperm in glucose-free BWW medium induces a significant number of acrosome reactions within minutes. The simultaneous addition of micromolar concentrations of ZnCl2 (25-1000 microM) potentiates the cGMP effects. Mid-micromolar concentrations were able to dramatically increase the percentage of acrosome reactions by a factor of 6.5 over 8 bromo cGMP alone. The induction of acrosome reactions was dependent upon external Ca++, and it is suggested that in this species Zn++ functions by affecting cyclic nucleotide metabolism and/or Ca++ flux.     

Innervation of the guinea pig spleen studied by electron microscopy

The innervation of the guinea pig spleen was investigated by electron microscopy. Unmyelinated nerve fibers in the capsulotrabecular and arterial systems were found to contain large and small granular and small agranular synaptic vesicles in their terminals and are thought to be sympathetic adrenergic in nature. They influence the contraction of the smooth muscle cells by diffusion innervation in these systems. These nerve terminals were also scattered in both the red and the white pulp. Pulp nerves wrapped by Schwann cells were further enclosed by myofibroblastic reticular cells. This condition revealed that the pulp nerves pass through the connective-tissue spaces of the reticular fibers, which contain elastic fibers, collagenous fibrils, and lamina densa-like materials of the usual basement laminae. One of the target cells for the pulp nerves is considered to be the myofibroblastic reticular cell in the reticular meshwork. Neurotransmitter substances released from the naked adrenergic nerve terminals travel through the reticular fibers and may play a role, by both close association innervation and diffusion innervation, in the contraction of reticular cells to expose the reticular fibers. At the exposed sides, connective-tissue elements of the reticular fibers are bathed with blood plasma, and the included naked nerve terminals, devoid of Schwann cells but with basement laminae of these cells, face free cells at some distance or are in close association with free cells, especially lymphocytes, macrophages, and plasma cells. The close ultrastructural relationship between the naked adrenergic nerve terminals and immunocytes strongly suggests that there is an intimate relationship between the immune system and the sympathetic nervous system through both close association innervation and diffusion innervation. Thus splenic adrenergic nerves of the guinea pig may play a triple role in 1) contraction of smooth muscle cells to regulate blood flow in the organ, 2) induction of the exposure of reticular fibers by contraction of the reticular cells in order to form a close relationship of the nerve terminals with the immunocytes, and 3) subsequent neuroimmunomodulation of the immunocytes.