Currently, my dissertation research consists of an examination of renal function and hormonal regulation of metabolism in postweaned northern elephant seal pups. Because elephant seal pups have adapted to fasting for 2.5 - 3 months postweaning, they provide an interesting model to address the issues of water and electrolyte homeostasis and endocrine regulation during a protracted fasting period. Some data exists on renal function and endocrine changes during periods of food restriction and fasting in pinnipeds, however some of these data are not conclusive and the physiological mechanisms involved are not well defined. Our previous data showed a decrease in plasma vasopressin (AVP) along with a decrease in urine output and increased urine osmolality. This apparent paradox in AVP concentrations and urine output will be addressed in my current research.
Ortiz RM, SH Adams, DP Costa and CL Ortiz. 1996. Plasma vasopressin levels and water conservation in fasting, postweaned northern elephant seal pups (Mirounga angustirostris). (pdf 412 Kb) Marine Mammal Science 12(1): 99-106.
Ortiz RM, CE Wade and CL Ortiz. 2000. Prolonged fasting increases the response of the renin-angiotensin-aldosterone system, but not vasopressin levels, in postweaned northern elephant seal pups. (pdf 63 Kb) General and Comparative Endocrinology 119: 217-223.
Ortiz RM, CE Wade and CL Ortiz. 2000. Effects of prolonged fasting on plasma cortisol and TH in postweaned northern elephant seal pups. (pdf 147 Kb) American Journal of Physiology: Regulatory, Integrative, and Comparative Physiology 280: R790-R795.
Research for my Master of Science thesis conducted at Texas A&M University focused on water flux and osmoregulation in West Indian manatees. Previous studies had suggested that West Indian manatees could actively drink salt water (mariposia) based on urine data, their renal anatomy, and their occurrence in marine habitats for extended periods. Because West Indian manatees inhabit both fresh water and marine environments, they provided an ideal model to address the questions of water balance and osmoregulation in marine mammals. Through a series of manipulations with fresh and salt water, we were able to demonstrate that manatees do not actively drink salt water, and that incidental ingestion of salt water during feeding elicited typical mammalian endocrine responses resulting in excretion of the excess salt load. However, captive animals consumed large amounts of fresh water (photo above), which could make them susceptible to hyponatremia if access to a source of salt is not provided.
Ortiz RM, GAJ Worthy and DS MacKenzie. 1998. Osmoregulation in free ranging and captive West Indian manatees (Trichechus manatus). (pdf 720 Kb) Physiological Zoology 71(4): 449-457.
Ortiz RM, GAJ Worthy and FM Byers. 1999. Estimation of water turnover rates of captive West Indian manatees (Trichechus manatus) held in salt and fresh water. (pdf 38 Kb) The Journal of Experimental Biology 202(1): 33-38.
Ortiz RM, DS MacKenzie, GAJ Worthy. 2000. Thyroid hormone concentrations in captive and free-ranging West Indian manatees (Trichechus manatus). (pdf 53 Kb) The Journal of Experimental Biology 203 (23): 3631-3637.
As an undergraduate, I participated in a research project at Playa Nancite, Costa Rica on the physiology and behavior of "arribada" and non-arribada sea turtles. The project involved a number of graduate students under the sponsorship of Dr. David Wm. Owens at Texas A&M University. My task was to quantify predation on olive ridley sea turtles (above photo) at this nesting beach and to determine if this predatory activity had any reprocusions on this population of turtles. The list of animals predating on turtle eggs was extensive, however adult turtles were only attacked by American crocodiles. Predation of crocodiles on the sea turtles was low and probably would not have any negative consequences on this nesting population of sea turtles. Recently, I examined the effects of short-term fresh water exposure on water flux and aldosterone concentrations in captive Kemp's ridley sea turtles. Exposure to fresh water resulted in elevations in water turnover rates and decreases in plasma osmolality and electrolytes, however aldosterone concentrations and Na+:K+ ratio were not altered.
Ortiz RM, P Plotkin and DW Owens. 1997. Predation upon olive ridley sea turtles (Lepidochelys olivacea) by the American crocodile (Crocodylus acutus) at Playa Nancite, Costa Rica. (pdf 211 Kb) Chelonia Conservation and Biology 2(4):585-587.
Ortiz RM, RM Patterson, CE Wade and FM Byers. 2000. Effects of acute fresh water exposure on water flux rates and osmotic responses in Kemp's ridley sea turtles (Lepidochelys kempi). (pdf 87 Kb) Comparative Biochemistry and Physiology A 127: 81-87.
Space & Gravitational Physiology
With the advent of the construction of the International Space Station (ISS), studies on the effects of altered gravitational load induced by centrifugation (above photo) or simulated by other means (head-down tilt, water immersion, hindlimb suspension) will be of great importance. While at NASA's Ames Research Center, I participated in studies examining the effects of altered gravitational load on renal function, metabolism, and hormonal responses. These studies will help provide a better understanding of the effects of altered gravitational load on rats, which can hopefully be used as a suitable model by which effects on humans (astronauts) can be extrapolated. The predictive value of these studies may provide insight on the consequences of exposure to microgravity during spaceflight and the subsequent exposure to hypergravity upon re-entry to earth. Assessing the physiological responses to hypergravity induced by centrifugation is also important since a centrifuge onboard ISS may be used as a countermeasure to the adverse effects of microgravity.
Wade CE and RM Ortiz. 1997. Effects of habituated restraint on urinary cortisol levels in rhesus monkeys. (pdf 393 Kb) Contemporary Topics in Laboratory Animal Science 36 (5): 55-57.
Ortiz RM, TJ Wang and CE Wade. 1999. Influence of centrifugation and hindlimb suspension on testosterone and corticosterone excretion in rats. (pdf 762 Kb) Aviation, Space, and Environmental Medicine 70 (5): 499-504.
Ortiz RM, TJ Wang and CE Wade. 1999. Urea and osmotic excretion in rats exposed to chronic centrifugation. (pdf 752 Kb) Aviation, Space, and Environmental Medicine 70 (11): 1089-1095.
Wade CE, LA Baer, WA Belisle, RM Ortiz and MF Vasques. 1999. Deposition and renal handling of urinary electrolytes from rats during spaceflight. (pdf 714 Kb) Journal of Gravitational Physiology 6 (2): 25-32.
Ortiz RM and CE Wade. 2000. Water balance in rats exposed to chronic centrifugation. (pdf 140 Kb) Journal of Applied Physiology 89: 56-60.
Ortiz RM, CE Wade and E Morey-Holton. 2000. Urinary excretion of LH and Testosterone from male rats during exposure to increased gravity: Post-spaceflight and centrifugation. (pdf 436 Kb) Proceedings of the Society for Experimental Biology and Medicine 225: 98-102.
Wade CE, RM Ortiz and LA Baer. 2000. Increases in body mass of rats during space flight: Models and measurements. Aviation, Space, and Environmental Medicine 71(11): 1126-1130.
Ortiz RM and GAJ Worthy. 2000. Effects of capture on adrenal steroid and vasopressin concentrations in free-ranging bottlenose dolphins (Tursiops truncatus). (pdf 105 Kb) Comparative Biochemistry and Physiology A 125: 317-324.
Ortiz RM. 2001. Osmoregulation in marine mammals. The Journal of Experimental Biology 204 (11): 1831-1844 .
