CHANGING EFFECT OF ICV IL-1-BETA ON VASOPRESSIN RELEASE IN ANESTHETIZED, FEMALE RATS AT DIFFERENT STAGES OF LACTATION - ROLE OF PROSTAGLANDINS AND NORADRENALINE

Interleukin-1 beta stimulates oxytocin and vasopressin release in cons cious, male rats and causes a rise in blood pressure. These experiment s were done to. A) examine the effect of i.c.v. interleukin-1 beta (1 ng/mu l) on circulating levels of vasopressin in female rats at differ ent stages of lactation and B) determine if alpha-adrenergic mechanism s and/or prostaglandins were involved as mediators, Urethane-anaesthet ized nonlactating rats and rats at Day 7, 10, 20 and 26 of lactation w ere set up for arterial blood sampling and i.c.v. injections. One mL b lood samples were obtained in one min periods before, and at 1, 2.5, 5 , 10, 30, 60 and 120 min after the following treatments: i.c.v. treatm ent with either interleukin-1 beta (1 ng in 1 mu l PBS-BSA) or PBS-BSA (1 mu l) as a vehicle control; or i.c.v, treatment with interleukin-1 beta following pretreatment with either phentolamine (1.7 mu g/mu l i .c.v.) or indomethacin (1 mu g/l i.c.v.). As blood was sampled, isoton ic saline was infused (1 mL per min) and blood pressure was monitored to minimize any hypovolemic effects due to sampling, Extracted plasma was assayed using a specific vasopressin radioimmunoassay. Interleukin -1 beta i.c.v. stimulated the release of vasopressin above that elicit ed by PBS-BSA alone in non-lactating rats resulting in an approximate 1.2 to 2-fold increase in plasma hormone levels, Throughout the first half of lactation, vasopressin responsiveness to i.c.v, interleukin-1 beta treatment was markedly attenuated. In latter stages of lactation, the response recovered and resembled that of non-lactators around the time of weaning. Prostaglandins consistently mediate a stimulatory ac tion of interleukin-1 beta on vasopressin release whereas alpha-adrene rgic mechanisms mediate a depression of interleukin-1 beta-induced vas opressin release during the early to middle stages of lactation. It is possible that the depression in interleukin-1 beta-stimulation of vas opressin release in early to mid-lactation is conducive for nursing to occur and that the increase in vasopressin responsiveness towards the latter stages of lactation represents a component of the weaning proc ess.