Journal of Applied Physiology AJP: Lung Cellular and Molecular Physiology
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J Appl Physiol 71: 150-158, 1991;
8750-7587/91 $5.00
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Journal of Applied Physiology, Vol 71, Issue 1 150-158, Copyright © 1991 by American Physiological Society

ARTICLES

Developmental changes in effects of histamine on segmental pulmonary vascular resistances

J. B. Gordon, S. Clement de Clety and K. Chu
Department of Pediatrics, Montreal Children's Hospital, Quebec, Canada.

In mature animals histamine infusion typically causes an H1-mediated increase and H2-mediated decrease in pulmonary vascular resistance (PVR). Moreover, low histamine concentrations can cause H1-mediated relaxation of vascular strips in mature animals, and in newborn animals histamine infusion causes only H1-mediated decreases in PVR. The mechanisms responsible for the different H1-mediated responses are unknown. We used an inflow-outflow occlusion technique to identify the sites of H1- and H2-mediated responses in lungs of developing lambs. Histamine was infused at 1.0 and 10.0 micrograms.kg-1.min-1 in control and H1- and H2-blocked lungs of newborn and juvenile lambs under "normoxic" and hypoxic conditions and in hypoxic H2-blocked lungs of mature sheep. In newborns histamine caused significant H1-mediated decreases in resistance across the arterial (delta Pa) and middle (delta Pm) segments of the circuit during both normoxia and hypoxia. In normoxic juveniles low-dose histamine caused H1-mediated decreases in the resistance across delta Pa and delta Pm, but the resistances across delta Pm rose above baseline at the higher dose. The venous segment exhibited only a high-dose increase in resistance. During hypoxia, the high-dose H1-mediated pressor response of delta Pm was attenuated compared with that during normoxia; however, the increase in venous resistance was unaffected. In hypoxic mature sheep, no low dose H1-mediated decrease in segmental resistances was seen, but at the higher dose an increase in all resistances occurred.(ABSTRACT TRUNCATED AT 250 WORDS)




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