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Study of an unselected population of adult laboratory rats demonstrates the presence of globule leucocytes in the bronchioles, bronchi, trachea, larynx and oropharynx. In the digestive tract, these leucocytes are seldom found in the anbal part of the stomach but are abundant in fhe glandular stomach where they have been confused with mast cells. Numerous globule leucocytes also occur in the large and small intestines. Although most of these leucocytes are located in the epithelium rather than the connective tissue of the mucous membranes of these organs, this pattern is reversed in the small intestine of normal rats. Globule leucocytes are present in essentially normal numbers in the trachea and larynx of axenic rats, but are less abundant than normal in the small intestine of these animals. The fine structure of the globule leucocyte and its characteristic inclusions is compared with that of other similar or possibly related cells and with described recently by Toner.

Chronic intermittent electrical stimulation (15 min on, 85 min off, seven times per day) eliminated endothelial dysfunction of pre-capillary arterioles in ischaemic rat ankle flexor muscles. Responses to acetylcholine were restored from constriction to dilation, and the reduced dilation to bradykinin was corrected by 1 week of stimulation. Administration of the NOS inhibitor N^ω-nitro-L-arginine for 1 week impaired arteriolar reactivity in a similar way to ischaemia, and dilator function was likewise restored by chronic stimulation. This suggests that nitric oxide production in the microcirculation is depressed by chronic ischaemia and that chronic electrical stimulation can specifically reverse this deficit. Stimulation applied to ischaemic muscles for 2 weeks also increased the numbers of microvessels immunostained for α-smooth muscle actin and the numbers of eNOS-positive microvessels and capillaries. These findings help to elucidate the mechanism of the beneficial effect of exercise in the treatment of peripheral vascular diseases by showing that muscle activity can improve both function and structural capacity of the microvasculature.

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