Structure-activity relationships of the vasopressor activity of canine peptide-A from fibrinogen.

Canine peptide-A was demonstrated to be an active vasopressor substance. The effect of intravenous injection of canine peptide-A was a prolonged rhythmic vasoconstriction and is unlike any previously described vasopressor peptides. The intravenous administration of canine peptide-A resulted in a maximum increase in mean blood pressure of 19.0 mm of mercury at a dose level of 2.5-10-minus 2 mumol. This pressor effect exhibited a log proportionality to the injected dose of peptide. The duration of the vasopressor effect was 30 min or greater. A rhythmic variation in pressor response was also observed in all experiments. The canine AP and B peptides were inactive when tested under the same conditions. The relationship between structure and biological activity was investigated. Structural degradation of half of the peptide molecule was performed without loss of vasopressor activity. The canine peptide-A is postulated as assisting in local hemostasis by vasoconstriction.     

Prey feeding increases water stress in the omnivorous predator Dicyphus hesperus

The effects of water stress (produced by water deprivation and prey feeding) on plant feeding were investigated in the omnivorous predator Dicyphus hesperus Knight (Hemiptera: Miridae). The objective was to determine if prey feeding aggravated water deficits and thus increased plant feeding. We measured plant feeding in a factorial experiment where female D. hesperus were prepared for experiments by providing or withholding water and/or prey for 24 h. We then evaluated the amount of plant feeding on Nicotiana tabacum seedlings by the direct observation of insects at three different densities of the prey, Ephestia kuehniella eggs. The amount of plant feeding, as measured by frequency of plant feeding bouts and time spent plant feeding during observation, was significantly greater for water‐deprived individuals than for those that had been provided with water. Individuals that had been provided with prey fed on plants at a significantly higher frequency than prey‐deprived individuals at two of the prey densities used in the experiment. These results support the hypothesis that plant feeding in zoophytophagous Hemiptera facilitates prey feeding by providing water that is essential for predation.