Effects of dehydration on cardiovascular development in the embryonic American alligator (Alligator mississipiensis).
ABSTRACT Effects of dehydration on reptilian embryonic cardiovascular function are unknown. Here, we present the first morphological and physiological data quantifying the cumulative effects of four acute dehydration events on the embryonic American alligator, Alligator mississipiensis. We hypothesized that dehydration would alter embryonic morphology, reduce blood volume and augment the response to angiotensin II (Ang II), a key osmotic and blood volume regulatory response element in adult vertebrates. Drying events at 30%, 40%, 50%, and 60% of embryonic incubation reduced total egg water content by 14.43 ± 0.37 g, a 3.4 fold increase relative to controls. However, embyronic blood volume was greater in the dehydration group at 70% of embryonic incubation compared to controls (0.39 ± 0.044 mLg(-1) and 0.22 ± 0.03 mLg(-1), respectively), however, both groups were similar at 90% of incubation (0.18 ± 0.02 mLg(-1) in the controls and 0.23 ± 0.03 mLg(-1) in the dehydrated group). Dehydration altered the morphological phenotype and resulted in an overall reduction in embryonic mass at both incubation time points measured. Dehydration also altered the physiological phenotype, resulting in embryonic alligators that were relatively bradycardic at 90% of incubation. Arterial Ang II injections resulted in a dose dependent hypertension, which increased in intensity over the span of incubation studied. While progressive incubation altered the Ang II response, dehydration had no impact on the cardiovascular responses to the peptide. Quantification of Ang II type-1 receptor protein using western blot analysis illustrated that dehydration condition and incubation time point did not alter protein quantity. Collectively, our results show that dehydration during embryonic development of the American alligator alters embryonic morphology and baseline heart rate without altering arterial pressure and response to Ang II.
- [Show abstract] [Hide abstract]
ABSTRACT: Using embryonic chickens (Gallus gallus domesticus), we examined the role of the renin-angiotensin system (RAS) in cardiovascular and osmotic homeostasis through systemic, chronic captopril injection, an angiotensin-converting enzyme (ACE) inhibitor. Captopril (5mgkg(-1) embryo wet mass) or saline (control) was delivered via the egg air cell daily from embryonic day 5-18. Mean arterial pressure (MAP), heart rate (ƒH), fluid osmolality and ion concentration, and embryonic and organ masses were measured on day 19. Exogenous angiotensin I (ANG I) injection did not change MAP or ƒH in captopril-treated embryos, confirming ACE inhibition. Captopril-treated embryos were significantly hypotensive, with MAP 15% lower than controls, which we attributed to the loss of the vasoconstrictive ANG II action. Exogenous ANG II induced a relatively greater hypertensive response in captopril-treated embryos compared to controls. Changes in response to ANG II following pre-treatment with phentolamine (α-adrenergic antagonist) indicated a portion of the ANG II response was due to circulating catecholamines in captopril-treated embryos. An increase in MAP and ƒH in response to hexamethonium indicated vagal tone was also increased in the absence of ACE activity. Captopril-treated embryos had lower osmolality, lower Na(+) and higher K(+) concentration in the blood, indicating osmoregulatory changes. Larger kidney mass in captopril-treated embryos suggests disrupting the RAS system may stimulate kidney growth by decreasing resistance at the efferent arteriole and increasing the fraction of cardiac output to the kidneys. This study suggests that the RAS, most likely through ANG II action, influences the development of the cardiovascular and osmoregulatory systems.Comparative Biochemistry and Physiology - Part A Molecular & Integrative Physiology 08/2014; in press. · 2.37 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: For various reasons, reduction or cessation of feeding (anorexia) can occur in either sex during periods of reproduction among vertebrates, from cichlids to elephant seals. Anorexia is commonly associated with gestation in snakes. Using radiotelemetry, we investigated the feeding and spatial ecology of a live-bearing viperid snake, the western diamond-backed rattlesnakes (Crotalus atrox). Specifi-cally, from 2001 to 2010, we determined the feeding frequency and home range size of adult females (n = 27) during the active season (March–October) in a popula-tion from the Sonoran Desert of Arizona. We addressed a central hypothesis: Do hunting and feeding occur throughout pregnancy? Also, we tested a corollary hypothesis: Does pregnancy influence home range size? We documented hunting and feeding from March to October and during pregnancy (June to mid-September). Feeding frequency was significantly greater in late pregnancy, a result that is in sharp contrast to most other large-bodied vipers. Furthermore, home range sizes in gestating subjects did not differ from those in nonreproductive years. Births occurred from mid-August to mid-September and mean litter size was 3.4. Frequent feeding in C. atrox during gestation unquestionably provides energy and nutrients to the mother, which is likely important for survival, but such food consumption does not imply that nutrients are used by the fetuses. There is, however, recent evidence in other snakes, including a pitviper, that amino acids are transferred to fetuses. Feeding during pregnancy in C. atrox may be important for both income and capital mode reproduction. Hunting and feeding throughout gestation might be accomplished by having relatively small litters not burdened by a body cavity filled with fetuses. Reduction in litter size may thus be a life-history (fecundity) trade-off that permits females to survive and maintain pregnancy in regions where drought and high temperatures are often extreme and chronic.
- [Show abstract] [Hide abstract]
ABSTRACT: Environmental conditions play a major role in shaping reptilian embryonic development, but studies addressing the impact of interactions between chronic and acute environmental stressors on embryonic systems are lacking. In the present study, we investigated thermal dependence of cholinergic and adrenergic cardiovascular tone in embryonic American alligators (Alligator mississippiensis) and assessed possible phenotypic plasticity in a chronic hypoxic incubation treatment. We compared changes in heart rate (f H) and mean arterial blood pressure (P M) for chronically hypoxic and normoxic-incubated embryos after cholinergic and adrenergic blockade following three different acute temperature treatments: (1) 30 °C (control incubation temperature), (2) acute, progressive decrease 30-24 °C then held at 24 °C, and (3) acute, progressive increase 30-36 °C then held at 36 °C. f H progressively fell in response to decreasing temperature and rose in response to increasing temperature. P M did not significantly change with decreasing temperature, but was lowered significantly with increasing acute temperature in the normoxic group at 90 % of development only. Propranolol administration (β adrenergic antagonist) produced a significant f H decrease at 24, 30, and 36 °C that was similar at all temperatures for all groups. For normoxic-incubated embryos at 90 % of development, atropine administration (cholinergic antagonist) significantly increased f H in both 24 and 36 °C treatments, but not in the 30 °C control treatment. This atropine response at 24 and 36 °C demonstrated acute thermally dependent cholinergic tone on f H late in development for normoxic-incubated, but not chronically hypoxic-incubated embryos. Collectively, data indicated that cardiovascular control mechanisms in embryonic alligators may be activated by thermal extremes, and the maturation of control mechanisms was delayed by chronic hypoxia.Journal of Comparative Physiology B 04/2013; · 2.02 Impact Factor