Robert S. McCuskey

Studies of the hemopoietic microenvironment. VII. Neural mechanisms in splenic microvascular regulation in mice.

Abstract The influence of the nervous system on the humoral regulation of the splenic microvasculature was evaluated using in vivo microscopic methods. Mice were anesthetized with sedative doses of pentobarbital which resulted in a condition during which sympathetic nerves could be excited both electrically and pharmacologically. A variety of vasoactive substances was administered topically or intraperitoneally with and without catecholamine depletion by reserpine, and the microvascular responses were measured using in vivo microscopic methods. The results, when considered along with those obtained previously [Reilly and McCuskey (1977) , Microvasc. Res. 13 , 79–90] using urethane anesthesia (nerves unresponsive to electrical stimulation), suggested: (1) the presence of innervated α-receptors on arterioles; (2) that the α-receptor is the predominant receptor in the mouse splenic microvasculature and its activation results in vasoconstriction; (3) that lactic acid, histamine, and prostaglandin E 2 and F 2α cause α-mediated arteriolar constriction by releasing stored catecholamine from sympathetic nerves; and (4) that subthreshold quantities of neurotransmitter may modulate microvascular sensitivity to agonists and antagonists in the presence of sympathetic nerves responsive to electrical stimulation.

Dynamic microscopy anatomy of the fetal liver. I. Microcirculation.

an understanding of this organ in life, a motion picture film was presented at the Fourteenth Microcirculatory Conference which illustrated the dynamic microscopic anatomy of its microvascular system in situ.1 This film was the initial record of an investigation now in progress, the goal of which is to elucidate the dynamic microscopic anatomy and physiology of the fetal hepatic microvascular system, especially as it is related to erythropoiesis.

Studies of the hemopoietic microenvironment: VI. Regulatory mechanisms in the splenic microvascular system of mice

Abstract Erythropoietin is reported to cause a functional hyperemia in the erythropoietic spleen of the mouse. The mechanism for this response was not clear since pharmacologic responses of the splenic microvascular system are poorly understood. Accordingly, various concentrations of several vasocative substances alone or in combination with appropriate blocking agents were administered topically to the spleens of mice while changes in the microvasculature were measured using in vivo microscopic methods. The results suggested the presence of both α- and β-adrenergic receptors in arterioles and the absence of such receptors in venules. Cholinergic receptors were sparse or absent throughout the microvasculature. Histamine elicited arteriolar dilation which was antagonized by metiamide, suggesting the presence of H 2 receptors in these vessels. Serotonin elicited only venular constriction. Lactic acid caused arteriolar constriction; bradykinin and prostaglandins (PG) E 2 and F 2α elicited arteriolar constriction, but only at high concentrations. The microvascular response to lactic acid and PG E 2 and F 2α was partially or completely antagonized by blockade of α receptors. Histamine, bradykinin, serotonin, and PG E 2 and F 2α caused a reduction in blood flow through the red pulp. While adenine nucleotides, guanosine, inosine, sodium phosphate, and potassium chloride elicited no response, adenosine was a potent vasodilator. This dilation was not blocked by adrenergic or cholinergic antagonists. Of the substances studied, only histamine, isoproterenol, and adenosine induced arteriolar dilation. Of these, only isoproterenol and adenosine increased the linear velocity of blood flow and the number of vessels with flow in them. Since no known β agonist occurs naturally in the spleen and adenosine was the most potent arteriolar dilator in physiologic doses, adenosine is suggested to be a possible candidate for the functional hyperemia reported in the erythropoietically stimulated murine spleen.

Erythropoietin: effect on the living fetal hepatic microvascular system in situ.

Abstract Microscopic examination of the effect of erythropoietin on the living fetal hepatic microvascular system in situ demonstrated that erythropoietin, in addition to its action on erythrocytopoiesis, effects the release of mature and maturing erythroid cells from the sinusoids into the peripheral circulation by dilating the sinusoid sphincters.

Studies of the Hemopoietic Microenvironment. V. Erythropoietin-lnduced Release of Vasoactive Substance(s) from Erythropoietin-Responsive Stem Cells

Summary Alterations in the splenic mi-crocirculation which accompany the suppression and recovery of CFU and ERC were studied in mice treated with Myleran and in polycythemic mice treated with Myleran and Ep. During the time of suppression of ERC by Myleran in nonpolycy-themic mice, blood flow was reduced significantly. Flow returned to normal during the time when repopulation of ERC was occurring but CFU was still suppressed. Administration of a split dose of Ep 3 days apart to polycythemic mice treated with Myleran resulted in dramatic increases in flow 24 hr after the first injection of Ep, with no increases in 59Fe incorporation in the blood. The microvascular response was nearly abolished by 48 hr after this injection. The second injection of Ep elicited limited increases in blood flow 24 hr later, accompanied by increases in 59Fe uptake. These results suggest that the effect of Ep on the splenic microvasculature is indirect and mediated by a vasoactive substance(s) released from replicating ERC following stimulation by Ep.

The Effect of Cellular Aggregation On Pressure-Flow Relationships in the Microvascular System

aggregation on the gross and microvascular systems.2 With the modification of the capacitance nanometer by Rappaport3 it became possible to me this equipment for recording the dynamic pressures in small blood vessels. Irwin4 and I3loch,5 using such equipment, have shown that it was possible to obtain dynamic pressure pulses of the microvascular system with cannulas as small as 30 jn and were able to obtain continuous recordings for hours. For the past seven years they have tested the equipment and have described its advantages and limitations. 6

Microscopic Observations of the Living Fetal Hepatic Microvascular System "in Situ"

tus, dysproteinemia and presenile vascular disease with hypercholesterolemia). A 16mm Cine camera was mounted on a (Leitz) ophthalmic head rest and focusing stand. A synchronized strobe light and focus light were mounted at 45° to the lens tube 6&dquo; length (lens 40 mm) . The magnification on the film was 5 X. The film rate was 24 to 32 pps. Film was fine grain TV recording film. The entire unit was mounted on a mobile over-bed table for studies at the bedside. Four scenes of 5 sec. each were recorded. The procedure was innocuous. Normal subjects revealed more rapid and uniform flow than the patients studied. Vascular tortuosity was negligible in normal subjects; in patients it ranged from slight tortuosity to multiple kinking and convolutions. Shunting was uncommon in normals, common in the patients studied, to the point of a honeycombing effect. Flow velocity varied directly as a function of vessel size in normals, averaging in venules of 75 to 90 tt in diameter, 400 ± 25 ///sec. In disease, flow patterns and velocities were extremely variable and did not follow any relationship to vessel size. Some large venules, 100 tt in diameter, revealed total stasis while smaller adjacent vessels often revealed above normal velocities. Areas of shunting and new vessel proliferation generally had slower than normal flow velocities. Vasoconstriction produced by cold, or cell aggregation produced by a fatty meal, resulted in retarded flow. The severity of the disease process correlated well with the degree of vessel abnormality and flow retardation.

Development of the innervation of fetal mesenteric microvasculature.

SummaryThe innervation of the mesenteric microvasculature was studied in fetal and neonatal rabbits with the aid of methods demonstrating fluorescence of catecholamines and cholinesterase activity as well as a silver impregnation procedure. The results showed that: (1) adrenergic nerve fibers were present, coursing independently in the mesentery by day twenty-one of gestation, and were found routinely in the adventitia of arterioles and venules by day 25 of gestation; (2) cholinesterase positive cells and fibers of the myenteric plexus were present by day 18 of gestation but cholinergic fibers were not present in the mesentery until day 26; the latter not being associated with blood vessels; and (3) nerve fibers in the mesentery thought to be sensory stained positively with the Holmes silver method on day 18 of gestation.