The involvement of the sympathetic nervous system in the centrogenic pressor and tachycardiac effects of prostaglandins E2 and F2 alpha in anaesthetised cats

Changes in plasma catecholamine levels following injection of prostaglandin F2alpha into the basal cistern in rabbits

We measured plasma epinephrine and norepinephrine concentrations in a rabbit model simulating subarachnoid hemorrhage (SAH), following the injection of prostaglandin F(2alpha) (PGF(2alpha)) into the basal cistern. In this model, plasma epinephrine values increased significantly (to 4.2-fold those before injection), substantially more than norepinephrine (which increased 1.3-fold) at 5 minutes (min) after PGF(2alpha) injection. Dissection of autonomic outflow from the cervical spinal cord or ligation of the suprarenal veins reduced the changes in plasma catecholamine concentrations associated with PGF(2alpha) injection. These results suggest that the sympathetic discharge seen after PGF(2alpha) injection into the basal cistern in rabbits occurred through the sympatho-adrenal pathways.

Developmental changes in respiratory, febrile, and cardiovascular responses to PGE(2) in newborn lambs

PGE(2) has centrally mediated respiratory, febrile, and cardiovascular effects that markedly differ between fetal and adult life. We hypothesized that the transition from fetal to adult responses to PGE(2) occurs in the newborn period. Thus effects of an intracarotid infusion of PGE(2) (3 microg/min for 60 min) were determined in unanesthetized newborn lambs at 5, 10, and 15 days after birth. At 5 days, PGE(2) reduced central CO(2) sensitivity, reduced lung ventilation due to a decrease in breathing frequency, and induced hypercapnia. By 15 days, these effects of PGE(2) had waned significantly. In contrast, phasic (expiratory) thyroarytenoid muscle electromyogram activity, number of short apneas, and incidence of Biot periodic breathing were similarly increased at all three ages. PGE(2) induced a sustained fever at 10 and 15 days. Heart rate and mean arterial blood pressure were unchanged in contrast to marked increases observed by others in adults. Results showed that the transition from fetal to adult respiratory and febrile responses to PGE(2) occurs in early postnatal life, whereas adult cardiovascular responses develop later in life in sheep.

Distribution and characterization of cyclooxygenase immunoreactivity in the ovine brain

Evidence from tissue culture studies suggests that glial cells are the principal source of prostaglandins in the brain. We have used immunohistochemistry, Western blot analysis, and enzyme activity assays to localize cyclooxygenase (COX), the enzyme responsible for the conversion of arachidonic acid to prostaglandins, in situ in the normal ovine brain. We observed very few immunoreactive glial cells. In contrast, an extensive distribution of COX-like immunoreactive (ir) neuronal cell bodies and dendrites and a corresponding pattern of COX enzyme activity were observed. COXir neurons were most abundant in forebrain sites involved in complex, integrative functions and autonomic regulation such as the cerebral cortex, hippocampus, amygdala, bed nucleus of the stria terminalis, substantia innominata, dorsomedial nucleus of the hypothalamus, and tuberomammillary nucleus. Moderate populations were observed in other regions of the central nervous system implicated in sensory afferent processing, including the dorsal column nuclei, spinal trigeminal nucleus, and superior colliculus, and in structures involved in autonomic regulation, such as the nucleus of the solitary tract, parabrachial nucleus, and the periaqueductal gray matter. We did not observe COXir axons or terminal fields, however. Our results suggest that neurons may use prostaglandins as intracellular or perhaps paracrine, but probably not synaptic, mediators in the normal brain.