Diel oxygen uptake in Chaoborus punctipennis (diptera : culicidae)

Oxygen consumption (µl/ mg dry wt. · hr^–1 corrected to STP) in Chaoborus punctipennis was measured in a Gilson differential respirometer at two-hour intervals during 24-hour periods. Animals were held at controlled conditions similar to those at the time of collection. Respiration was measured under controlled temperatures and natural photoperiod. Measurements were begun about 36 hours after collection.Winter-collected animals showed a lower and more stable respiration than summer and fall-collected animals which did not differ from one another. Respiration increased with temperature becoming quite variable at 30°C where mortality was highest. Animals collected at different seasons and subjected to a variety of temperatures did not show a predictable pattern of respiration during the daily cycle under any condition tested.Since the 36-hour delay in respiration measurements could have dampened a diel cycle, oxygen consumption was determined within an hour of collection and followed for 24 hours. For this experiment animals were collected at six-hour intervals over a 24-hour period. Respiration did not show a predictable pattern of variation during the day-night cycle.This work was supported in part by a grant from Department of Interior, Office of Water Resources Research. All correspondence should be addressed to A.S. Tombes.     

Effects of vasoactive intestinal peptide on steroid secretion and plasminogen activator activity in granulosa cells of the hen

Studies were conducted to evaluate the effects of vasoactive intestinal peptide (VIP) on steroidogenesis and plasminogen-activator (PA) activity in isolated granulosa cells of the largest preovulatory (F1) follicle of the hen. Vasoactive intestinal peptide, but not avian pancreatic polypeptide, the chicken VIP fragment (16-28) or the VIP congener, PHM-27, induced a dose-related increase in progesterone and androgen secretion, with an apparent median effective dose (ED50) of 5.9 X 10(-7) and 5.7 X 10(-7) M, respectively. The effects of VIP were, at least in part, mediated by the adenylyl cyclase system in that cotreatment of cells with VIP and the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX), potentiated the steroidogenic effects. However, the time course of action for VIP on steroidogenesis was considerably slower than that for the gonadotropin, luteinizing hormone (LH), and this was attributed to a slower induction of cyclic adenosine 3',5'-monophosphate (cAMP) formation within granulosa cells. Finally, VIP was found to be a potent inhibitor of PA activity, and this inhibition was potentiated by coincubation of VIP with IBMX. We suggest that, in the hen, VIP has a direct and specific action on both steroidogenesis and PA activity, and that these actions are mediated, at least in part, by the adenylyl cyclase system. The comparatively slow induction of cAMP formation by VIP suggests that this peptide is involved in the control of cell differentiation and development rather than the ovulatory process.