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Biomedical subjects

K Ronald

Publications and source records attributed to K Ronald.

At least 37 records · Page 2Linked to original sources
PubMed1979

Structure of the testis in neonate and adult harp seals, Pagophilus groenlandicus.

The structure of the seminiferous tubules in neonate harp seals, Pagophilus groenlandicus, was essentially similar in one-, five- and ten-day old animals. The tubules were small in diameter, devoid of lumina and contained predominantly supportive cells. The interstitial cells in the neonates were large, numerous and highly vacuolated. They became smaller and appeared less active in the ten-day old animals compared with the one-day old seals, although they were still considerably more numerous and vacuolated than in testes taken from adult harp seals.

Aging↗
PubMed1979

Some aspects of temperature regulation in newborn harp seal pups.

Harp seals are born on the drifting ice of the North Atlantic Ocean during arctic winter when temperatures of -20 degrees C, occasionally in combination with wind of 10 m/s, might prevail for days. At birth the pups lack subcutaneous blubber and the wet infantile fur has a conductance value of 30.0 W . m-2 . degrees C-1, as compared with only 2.0 W . m-2 . degrees C-1 when dry. While still wet immediately after birth the pups are nevertheless able to retain body core temperature by shivering. This activity leads to reduction of muscle fat and glycogen stores. Nonshivering thermogenesis commences in thermogenic adipose tissue by virtue of loosely coupled mitochondria. Thermogenic adipose tissue is found at birth both as a subcutaneous layer along the back and as internal deposits around venous plexuses in the neck, on the pericardium, on the kidneys, and the abdominal walls. After about 3 days of suckling the subcutaneous adipose tissue loses its thermogenic function being gradually transformed into blubber, whereas the internal deposits persist at least until the pups venture into water at the age of 3-4 wk.

Adipose Tissue↗
PubMed1978

Structure of the Adenohypophysis in parturient female and neonate harp seals, Pagophilus groenlandicus.

The pars distalis of parturient harp seals (Pagophilus groenlandicus) is divisible into three distinct zones based on the major cellular components of the different regions. A clear zonation is lacking in neonate seals, the medical "basophilic wedge" and the anterior gonadotrophic were small and difficult to identify. Five cell types were identified based on cytological characteristics: somatotrophs, mammotrophs, thyrotrophs, gonadotrophs and stellate cells; corticotrophs could not be identified, with any certainty, in any of the preparations, nor could the gonadotrophs be classified into LH, FSH, and ICSH cells. The pars intermedia enlarged during the early post-partum period and was large in the parturient females.

Adrenocorticotropic Hormone↗
PubMed1978

Aspects of temperature regulation in harp seal pups evaluated by in vivo experiments and computer simulations.

Temperature regulation in harp seal pups (Pagophilus groenlandicus) has been studied by in vivo measurements of oxygen consumption, body temperatures and in vitro determinations of the thermal values of a fur sample. The experimental animals were restrained and exposed to natural wheather conditions. Solar irradiance above 600 W/m (global radiation) caused hyperthermia. Computer simulations based on the thermal values of the fur indicated that heat dissipation from primarily the limbs is a prerequisite for avoiding hyperthermia under natural weather conditions. Further simulations showed that the lower critical temperature of a lean newborn harp seal pup with standard metabolism is only--1 degree C while it is depressed to--59 degree C as the pup grows, aquire a 10 cm thick layer of blubber and the metabolism increases to 1.5 times standard. High metabolism and tolerance to low deep body temperatures (35 degree C) seems a prerequisite for thermal balance in the harp seal pup under cold conditions.

Animals↗
PubMed1977

Methylmercury poisoning in the harp seal (Pagophilus groenlandicus).

Hematological and blood chemistry values were examined in harp seals (Pagophilus groenlandicus) exposed to daily oral dosages of methylmercuric chloride (MMC). Two seals, exposed to 0.25 mg MMC/kg body weight/day for 60 and 90 days, respectively, did not show abnormal blood values. Two other seals exposed to 25.0 mg MMC/kg body weight/day died on day 20 and 26 of exposure. Blood parameters indicated toxic hepatitis, uremia and renal failure. Total mercury and methylmercury values in the tissues of the experimental animals indicated that harp seals can tolerate high levels of mercury in the brain and that the observed renal and hepatic dysfunction were related to the high accumulation of mercury in these tissues. Tests of renal function are useful in cases of severe methylmercury poisoning.

Animals↗
PubMed1976

Organochlorine and mercury residues in the harp seal (Pagophilus groenlandicus).

Samples of blubber, liver, kidney and brain, obtained from 10 male, 6 female neonatal, and 4 lactating female harp seals (Pagophilus groenlandicus), were analysed for DDT, dieldrin, PCB, and total mercury. Methyl mercury levels in blood were also determined. Biocide deposition was not significantly different in female and male ten day old pups. There were no significant differences in biocide levels in the liver of the 14/+ day old males, but in blubber there were significant differences in dieldrin and DDT. There was no clear relationship between biocide levels in the 6-18 year old lactating adults and their pups. Younger adult seals (6 and 7 years) were found to have higher levels of PCB and sigmaDDT levels in their blubber than did older females (10 and 18 years). Wide intraspecific variation was noted in organochlorine and mercury residue levels. Pups taken in 1973 were found to have lower organochlorine residues than pups taken in the same area in 1971. Preliminary investigation indicates that detectable amounts of organochlorine and mercury residues are capable of crossing the placenta in the harp seal.

Adipose Tissue↗
PubMed1975

The harp seal, Pagophilus groenlandicus (Erxleben, 1777). XVII. Structure and metabolic adaption of the caval sphincter muscle with some observations on the diaphragm.

Three types of fibre, dark (type 1), light (type 2) and intermediate, were distinguished in the caval sphincter muscle of the diaphragm in the harp seal (Pagophilus groenlandicus) using histochemical and electron-microscopic techniques. The dark fibre contained large peripheral aggregations of mitochondria, numerous lipid droplets and dense aggregates of glycogen granules. The same features were observed in the dark fibre of the diaphragm muscle too. In the light of the low oxidative enzyme activity and high lipase activity observed in the diaphragm and other skeletal muscles of the harp seal in previous studies, it is postulated that these mitochondrial aggregations and lipid droplets represent an adaptation for the generation of heat through non-shivering thermogenesis comparable to that in the brown adipose tissue. Such ability to generate and maintain heat by uncoupling the oxidative phosphorylation process should enable the caval sphincter muscle to function efficiently in regulating the cardiac return of blood from the inferior vena cava during a dive when the body temperature as a whole drops. The lack of the regional differences in the fibre composition of the harp seal diaphragm, as were reported in the rat diaphragm, is attributed to the seal's large body size, lower metabolic rate and diving habit.

Animals↗