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Biomedical subjects

J E Austin

Publications and source records attributed to J E Austin.

At least 19 recordsLinked to original sources
PubMed2001

Duck populations as indicators of landscape condition in the Prairie Pothole Region.

The Prairie Pothole Region of the northern Great Plains is an important region for waterfowl production because of the abundance of shallow wetlands. The ecological significance of the region and impacts from intensive agriculture prompted the U.S. Environmental Protection Agency to select it as one of the first areas for developing and evaluating ecological indicators of wetland condition. We examined hypothesized relations between indicators of landscape and wetland conditions and waterfowl abundance on 45 40 km2 study sites in North Dakota for 1995-1996. Landscape condition was defined a priori as the ratio of cropland area to total upland area surrounding wetlands. Measures of waterfowl abundance included estimated numbers of breeding pairs (by species and total numbers) and gamma, a species-specific correction factor which effectively adjusts breeding pair estimates for annual or area-related differences in pond size. Landscape indicators and waterfowl measures varied among regions. Results indicated that most areas in the Coteau region are of much higher quality for ducks than those in the Drift Plain, and areas in the Red River Valley are of the poorest quality for ducks. Regression models demonstrated the impact of agricultural development on breeding duck populations in the Prairie Pothole Region. The most consistent landscape indicators of waterfowl abundance were percent of cropland and grassland. Models were inconsistent among years and species. The potential biotic indicators of landscape and wetland condition examined here would be appropriate for temporal trend analyses, but because of inherent geographic variability would not be appropriate for single-year geographic trend analyses without more extensive evaluations to improve explanatory models.

Agriculture↗
PubMed1992

Tryptophan analogues form adducts by cooperative reaction with aldehydes and alcohols or with aldehydes alone: possible role in ethanol toxicity.

Previous work showed that the exocyclic amino groups of nucleic acid components react quickly at ambient temperature with acetaldehyde and ethanol to yield mixed acetals [R-NH-CH(CH3)-O-C2H5]. We now find that the same type of reaction occurs readily with the nitrogen of 3-substituted indoles (e.g., indole-3-acetic acid and N-acetyltryptophan), analogues of the amino acid tryptophan. In contrast, unsubstituted indole reacts very rapidly at the carbon in ring position 2 or 3 with acetaldehyde to form bis(indolyl)ethane without ethanol entering into the reaction. Product structures have been confirmed by fast atom bombardment MS and 1H NMR. The former reaction occurs optimally in 30-50% aqueous solution below pH 4. It also proceeds more slowly and with reduced yields in aqueous media at more neutral pH. This reaction may be of biological concern, as it supplies a mechanism for protein modifications with possible toxic effects in human tissues where ethanol is metabolized.

Acetaldehyde↗
PubMed1986

Stimulation of tumor growth in adult rats in vivo during an acute fast.

These experiments investigate an increase in tumor growth that occurs in adult rats in vivo during an acute fast. The effects of feeding, fasting, and underfeeding on the growth of Morris hepatomas 5123C and 7288CTC in Buffalo rats and of Walker carcinoma 256 and Jensen sarcoma in Sprague-Dawley rats were studied. Animals were matched for tumor size and growth during a period of ad libitum feeding preceding the fasting or underfeeding. Tumor growth was documented by increased size and incorporation of [methyl-3H]thymidine into tumor DNA. Fasting increased the rate of growth of the tumors 3 to 4 times over that measured in fed rats. This effect began during the first day of fasting and ended abruptly on refeeding. After refeeding tumor growth slowed to the rate in fed rats. Tumors from fed or fasted rats were not different in cellularity or dry weight/g wet weight. A positive growth response in the tumor required lipolysis and ketosis in the host. No stimulation was observed during an acute fast in either immature rats or in mature rats whose weights had been reduced by underfeeding. These animals have small fat stores and show no increase in arterial blood free fatty acid or ketone body concentrations during an acute fast. Finally, underfeeding of adult rats raised the blood concentrations of these nutrients to values that were intermediate between those in fasted and fed rats. Tumor growth rates in these rats were intermediate between those in fasted and fed rats. The results support the proposal that an increase in availability of free fatty acids and/or ketone bodies is the stimulus that increases the rate of tumor growth during an acute fast.

Animals↗
PubMed1984

The effects of the WIC program on the growth of infants.

The Special Supplemental Food Program for Women, Infants and Children (WIC) provides food supplements and nutrition counseling to pregnant and lactating women and children up to age 5 who are at nutritional risk. The purpose of this study was to determine the effects of the program on the growth of infants. Retrospective longitudinal anthropometric data were obtained on 906 WIC and 1001 non-WIC infants from birth to 18 months of age. A new methodology was developed that addressed two factors in longitudinal studies frequently confounded with program impact: 1) regression to the mean and 2) expected growth. Regression analyses indicated that children who were on WIC between 6 and 18 months of age were growing at greater than expected rates. The most persistent program effect was at 6 months of age, after the children had been on the program for an average of 4 months. The study indicated that data routinely collected by the program can be used for evaluation purposes.

Body Weight↗
PubMed1983

Modulation of angiotensin II pressor responsiveness by circulating levels of angiotensin II in pregnant sheep.

During human and ovine pregnancy, systemic pressor responses to infused angiotensin II are decreased when compared to the nonpregnant state. An increased circulating level of angiotensin II has been proposed as one of the possible mechanisms responsible for this refractoriness. The present study was designed to determine if increased pressor responsiveness to exogenous angiotensin II occurs after circulating levels of angiotensin II in pregnant ewes are reduced. Pregnant (112 to 118 days' gestation) and nonpregnant sheep were instrumented with catheters in the femoral artery and vein. Dose-response curves to angiotensin I, angiotensin II, and norepinephrine were established prior to and during continuous short-term (2 to 3 hours' duration) and long-term (24 hours' duration) inhibition of angiotensin converting enzyme activity by either captopril or enalapril. Short-term infusions of converting enzyme inhibitors blocked the formation of angiotensin II from exogenously administered angiotensin I but did not alter pressor responsiveness to angiotensin II or norepinephrine in pregnant and nonpregnant sheep. Long-term infusions of the angiotensin converting enzyme inhibitor enalapril blocked responses to angiotensin I but did not alter pressor responses to norepinephrine in pregnant and nonpregnant sheep. In contrast, responses to angiotensin II were significantly potentiated in pregnant sheep but were not altered in nonpregnant sheep. These results suggest that increased circulating levels of angiotensin II in pregnant sheep are responsible for pregnancy-induced decreases in angiotensin II responsiveness.

Angiotensin II↗
PubMed1982

Effect of vasoactive intestinal polypeptide on uterine blood flow in pregnant ewes.

Vasoactive intestinal polypeptide has been localized in the uterine vasculature, uterine smooth muscle and the placenta of several species. Vasoactive intestinal polypeptide is a potent uterine vasodilator in nonpregnant sheep and also abolishes spontaneous uterine contractile activity, but the effects of this polypeptide on the uterine vasculature of the pregnant animal is currently unknown. The present experiments were performed in seven late-term pregnant sheep which were chronically catheterized to evaluate the uterine vascular effects of vasoactive intestinal polypeptide. An intra-arterial catheter was placed in a branch of the main uterine artery to allow administration of vasoactive intestinal polypeptide directly into the uterine vasculature. Uterine blood flow was continuously monitored via an electromagnetic flow transducer on both main uterine arteries. Vasoactive intestinal polypeptide infused at the rate of 1 to 30 micrograms/min produced dose-related reductions in uterine blood flow (33% +/- 9% at 30 micrograms/min). This decrease was due to a reduction in systemic arterial blood pressure, since calculated resistance in the uterine vasculature that received the vasoactive intestinal polypeptide did not change significantly. In addition, the contralateral uterine vasculature that did not receive direct intra-arterial infusions of vasoactive intestinal polypeptide showed identical changes. These data suggest that vasoactive intestinal polypeptide produces peripheral vasodilation at doses which have very little uterine effect locally. These data can be interpreted to mean either that high local endogenous production of vasoactive intestinal polypeptide prevents exogenously administered vasoactive intestinal polypeptide from exerting its vascular effects, or that vasoactive intestinal polypeptide is a very weak uterine vasodilator in pregnant ewes. The clarification of these possibilities will require further experimentation.

Animals↗
PubMed1982

Effect of bisenoic prostaglandins and arachidonic acid on the uterine vasculature of pregnant sheep.

Prostaglandins have been implicated as regulators of uteroplacental blood flow during pregnancy. However, the investigation of the vascular effects of these humoral agents has been extremely limited. The present study has evaluated the effects of intra-arterial infusions of prostaglandin D2, E2, F2 alpha, I2, 6-keto-F1 alpha, thromboxane B2, and bolus injections of the prostaglandin precursor arachidonic acid into the uterine vasculature of late-term pregnant ewes. Prostaglandins E2, F2 alpha, 6-keto-F1 alpha, and thromboxane B2 all reduced uterine blood flow, with prostaglandins E2 and F2 alpha being much more active. Since prostaglandins E2 and F2 alpha increase uterine tone, a portion of their vascular effects appears to be due to myometrial compression. In contrast, prostaglandins D2 and I2 produced dose-related increases in uterine blood flow in pregnant animals and did not alter uterine tone or contractile activity. Arachidonic acid produced dose-related increases in uterine vascular resistance in three out of five animals and had no effect in the other two animals. The differential vascular effects produced by the individual prostaglandins and their precursor suggest that the overall effect of these compounds on the uterine vasculature will depend on the summation of the individual actions.

Animals↗
PubMed1982

A model for studying chronic reduction in uterine blood flow in pregnant sheep.

A model is described for the investigation of the effects of acute and chronic reduction in uterine blood flow in unanesthetized pregnant sheep. An externally adjustable vascular occluder has been designed to utilize the principles of a modified Goldblatt clamp. This occluder is made of nonbreakable plastic and is adjusted via a flexible cable encased in a sheath. The occluder has been tested in 17 pregnant sheep and has remained functional for periods up to 36 days, the length of implantation. This occluder has allowed graded reductions in uterine blood flow, which can be accurately and consistently reproduced. An example of flow reduction is shown in which uterine blood flow has been reduced by 24, 47, and 82% in late-term pregnant sheep. This method will allow the investigation of the effects of uterine hypoperfusion and fetal hypoxia in a precisely controlled unanesthetized pregnant sheep preparation.

Animals↗
PubMed1982

Evaluation of the effect of WIC supplemental feeding on birth weight.

This study examined the impact of pregnant women's participation in a WIC supplemental feeding program on the birth weight of infants. Data on 1,328 WIC and non-WIC participants were collected from a retrospective review of medical and/or nutrition records. Participation of women in WIC was associated with a positive and significant increment in birth weight of their infants.

Adolescent↗
PubMed1981

Effect of bisenoic prostaglandins on the uterine vasculature of the nonpregnant sheep.

The effects of the bisenoic prostaglandins on the uterine vasculature and uterine contractile activity have been evaluated in an unanesthetized chronically catheterized nonpregnant sheep preparation. Changes in uterine blood flow were monitored with electromagnetic flow probes while uterine contractile activity and tone were determined via an intra-uterine balloon connected to a pressure transducer. Prostaglandins A2, D2, E2, and prostacyclin (PGI2) were all found to be vasodilators. PGD2 and PGI2 were much more potent than PGA2 and PGE2 in dilating the uterine vasculature. The prostacyclin breakdown product 6-keto PGF1 alpha, PGF2 alpha, thromboxane B2, and the endoperoxide analogues U44069 and U46619 produced vasoconstriction of the uterine vasculature. Prostaglandins A2, D2 and F2 alpha increased while PGI2 decreased uterine contractile activity. PGF2 alpha also increased uterine tone suggesting that a portion of its vasoconstrictor activity may be due to mechanical compression of the uterine vasculature.

Animals↗