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G A Parker

Publications and source records attributed to G A Parker.

At least 19 recordsLinked to original sources
PubMed1992

Mucinous biliary cystadenoma: a case report and review of the literature.

Mucinous biliary cystadenomas are rare neoplasms with protean manifestations. In most cases the mucinous material is retained within the cyst itself. We describe an asymptomatic case of a mucin secreting biliary cystadenoma in which the mucin presented as an amorphous intraluminal filling defect in the common hepatic duct on endoscopic retrograde cholangiopancreatography (ERCP). The neoplasm itself was confined to the posterior segment of the right hepatic lobe and was treated by formal right hepatic lobectomy. This case prompted a review of mucinous biliary cystadenomas.

Aged↗
PubMed1992

Intrathecal 5-fluorouracil in the rhesus monkey.

Because meningeal spread of both leukemia and solid tumors remains a difficult therapeutic problem, there is a compelling need to develop new agents for intrathecal administration. 5-Fluorouracil (5FU), an active anticancer agent, penetrates into the central nervous system to some degree following intravenous dosing. Significant systemic toxicity, however, is associated with this route of administration. Therefore, the pharmacokinetic behavior of 5FU following its intrathecal administration was studied in a rhesus monkey model. After a 10-mg intraventricular dose, the disappearance of the drug from ventricular cerebrospinal fluid was monoexponential, the half-life being 51 min; the area under the concentration-time curve (AUC) being greater than 18 mM h-1; and the peak ventricular 5FU concentrations ranging between 10 and 15 mM. After a 1-mg intralumbar dose, the AUC was 1235 microM h-1. No toxicity was observed following intraventricular administration of 5FU. After intralumbar administration of either a 10-mg or a 1-mg dose, however, local toxicity was observed in the lumbar spinal cord. These findings suggest that intrathecal administration of 5FU is not presently a feasible means of achieving cytotoxic cerebrospinal fluid concentrations.

Animals↗
PubMed1992

Formal hepatic resection of colorectal liver metastases. Ploidy and prognosis.

Fifty consecutive patients who underwent 52 formal hepatic resections (excluding isolated wedge resections) for metastatic colorectal cancer were analyzed to determine whether DNA content was of prognostic significance. The Dukes' stages of the colorectal primaries were: A (10%), B (20%), C (40%), D (28%), and unknown in 2%. Four patients whose liver metastases were discovered at the time of resection of the primary bowel cancer underwent concomitant liver resection, and the remaining patients underwent delayed resections. The hepatic resections performed were right lobectomy (50%), extended right lobectomy (19%), left lobectomy (13%), left lateral segmentectomy (6%), left lobectomy and right wedge (6%), extended left lobectomy (4%), and right lobectomy and left wedge (2%). The overall morbidity rate was 29%. The in-hospital mortality rate was 9%. As of November 1991, 36 patients have recurred. The 5-year actuarial survival was 28%. Flow cytometry could be performed on 37 archival specimens, 15 of which were found to be diploid whereas 22 were aneuploid. All metastases from Dukes A colorectal primaries demonstrated a diploid DNA content. In addition, there was no difference in actuarial survival between diploid and aneuploid tumors. These data suggest that in selected patients, formal hepatic resection of colorectal liver metastases can be performed with an acceptable morbidity rate, mortality rate, and survival, but ploidy of the resected tumor is not of prognostic significance.

Adult↗
PubMed1991

A model of constant random sperm displacement during mating: evidence from Scatophaga.

This paper extends the sperm displacement model of Parker et al. (Behav. Ecol. Sociobiol. 27, 55 (1990)), in which sperm displacement is viewed as a process in which one unit of sperm introduced displaces one unit of sperm from the female's sperm stores. Here this process is envisaged in terms of the change in density of sperm in the sperm stores. In matings with virgin females, only sperm store fluid is displaced at the start of sperm transfer, but if there is swift random mixing of seminal and sperm store fluid, the fluid displaced will contain sperm at the same average density as that in the sperm stores (random displacement). In mating of the same female by two or more males, the sperm density of the last male to mate is assumed to be independent of the presence of previous sperm; P2 (the proportion of eggs fertilized by the last male) thus equals the density of the last male's sperm divided by the current total density of sperm in the sperm stores. Once the sperm stores have reached the asymptotic density (equivalent to the input density, i.e. the density of sperm in the seminal fluid), the present model becomes equivalent to that of Parker et al. (1990). Predictions for this model are tested using all available data from the dung fly, Scatophaga stercoraria. They are based on the assumption that sperm are transferred at a constant rate with copulation time. The data concur with this model, and we conclude that it is better than various other simple alternatives for explaining P2 in Scatophaga.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Stability of acetazolamide in suspension compounded from tablets.

The stability of acetazolamide in an extemporaneous suspension compounded from tablets was studied. Acetazolamide 25-mg/mL suspension was prepared by levigating the comminuted 250-mg tablets with 70% sorbitol solution. The mixture was incorporated into a suspension vehicle containing magnesium aluminum silicate and carboxymethylcellulose sodium. Appropriate sweeteners, flavoring agents, preservatives, humectants, and pH adjusters were then added. The suspension was stored in amber glass bottles at 5, 22, 30, 40, and 50 degrees C. Samples were analyzed for the concentration of acetazolamide by stability-indicating high-performance liquid chromatography on days 3, 7, 11, 18, 24, 32, 42, 54, and 79. For batches stored at 5, 22, and 30 degrees C, the initial acetazolamide concentration was maintained during the entire 79 days of the study. However, the concentrations in the batches stored at 40 and 50 degrees C were below 90% of the initial value after 79 and 32 days, respectively. The Arrhenius plot was used to predict a shelf life of the suspension at room temperature of 371 days. Acetazolamide oral suspension 25 mg/mL was stable for at least 79 days at 5, 22, and 30 degrees C. The formulation should be maintained at pH 4-5 and stored in amber glass bottles.

Acetazolamide↗
PubMed1990

Local management of pancreatic carcinoma: iodine-125 implantation.

A retrospective review of patients with pancreatic carcinoma treated from 1983 to 1986 was performed. Group 1 comprise 11 patients judged surgically unresectable who were implanted with iodine-125 followed by external beam therapy post-operatively (Implant + XRT). Eight patients received external beam therapy alone (XRT) Group 2, and 23 patients underwent radical surgical resection (group 3). Median survival was 8 months in the implant + XRT group; 5 months in the XRT alone group and 7.5 months in the surgical group. Locoregional control was achieved in 8/11 (73%), 2/8 (25%), and 11/23 (48%) of these groups respectively. Pain was the most common presenting symptom, 38/42 (90%). Complete, lasting palliation was achieved in 8/10 (80%) of group one, 2/8 (25%) of group two, and 13/20 (65%) of group three patients. Despite surgical unresectability implant + XRT appears to offer similar results to radical surgery. The data are presented with respect to the implant technique, disappearance of the tumour on CT scan and patterns of failure.

Adenocarcinoma↗
PubMed1990

Naloxone in septic shock.

Treatment of septic shock is a persistent dilemma. The clinical use of agents such as naloxone has resulted in variable success. Because the dosage and timing of these agents are considered critical factors in their efficacy, we investigated both dosage and timing of naloxone. Thirteen consecutive patients with documented septic shock and resistance to a one-liter fluid challenge underwent invasive hemodynamic monitoring and the administration of naloxone by initial bolus of 0.03 mg/kg followed by infusion at a rate of 0.2 mg/kg.h over one hour. During the one-hour observation period, iv fluid administration, concomitant pressor agents, and respirator values were constant. After infusion, adjustments in fluid administration, respirator status, and pressor agents were made as required by the clinical situation. A significant increase in mean arterial pressure (MAP) over baseline (60 +/- 3 mm Hg) was noted at 5 min (77 +/- 6 mm Hg, p less than .005) and at 30 min (73 +/- 6 mm Hg, p less than .025). Similarly, a significant increase in systolic arterial pressure was noted over prenaloxone levels (89 +/- 3 mm Hg) at 5 min (114 +/- 6 mm Hg, p less than .001), 30 min (107 +/- 8 mm Hg, p less than .05), and at one hour (106 +/- 8 mm Hg, p less than .05). There was a moderate nonsignificant increase in cardiac index, pulmonary capillary wedge pressure, and systemic vascular resistance. No side-effects to naloxone were noted in our group. No effect on survival could be demonstrated. We found no overall effect on mortality. However, by its increase of MAP, naloxone may serve as a temporizing agent during the treatment of critically ill patients with septic shock.

Adult↗
PubMed1978

Selfish genes, evolutionary games, and the adaptiveness of behaviour.

The science of sociobiology, which began in principle with the work of Fisher and Haldane and has more recently been developed by Hamilton, Maynard Smith, Trivers, Wilson and others, has been the centre of both scientific and political controversy. Dr Parker discusses the strengths and weaknesses of the approach, and illustrates that behaviour can be adapted in a complex way in conformity with sociobiological theory.

Altruism↗
PubMed1978

Models of parent-offspring conflict. I. Monogamy.

Theoretical models for Trivers (1974) concept of parent-offspring conflict are examined for species in which the effects of the conflict are felt by full sibs. A rare conflictor gene will spread if (f(m) greater than 1/2(m + 1), where f(m) is the fitness gained by a conflictor relative to a non-conflictor offspring (f(m) greater than 1), and m is the amount of parental investment taken by a conflictor relative to m = 1 for a non-conflictor. The range of m alleles which can spread against the parent optimum decreases as the cost to the parent increases until a point is reached where there is no conflict of evolutionary interests. There would be no polymorphism for conflictor: non-conflictor alleles unless special conditions prevail. The conflictor allele which spreads most rapidly as a rare mutant against the parental optimum is not an evolutionarily stable strategy (ESS). The ESS for parent-offspring conflict in monogamous species has mo = f(mo)/2[df(mo)/dmo]. The analytical solutions are confirmed throughout by simulations.

Alleles↗
PubMed1978

Models of parent-offspring conflict. II. Promiscuity.

The population genetics of Trivers (1974) concept of parent-offspring is examined for species in which the effects of the conflict are felt by future half-sibs, as in promiscuous mating systems in which the male shows no parental care. Whether or not a rare conflictor gene will spread in a non-conflictor population depends on f(m) greater than (m + 1)/(0.5m + 1.5) for a dominant gene, and on f(m) greater than 1/4(7 + 3) for a recessive gene; f(m) is the fitness gained by a conflictor relative to a non-conflictor offspring [f(m) greater than 1], and m is the amount of parental investment taken by a conflictor relative to m = 1 for a non-conflictor. The ESS value for conflict (mo) in promiscuous species with zero male parental care has mo = f(mo)/4[df(mo)/dmo]. However, where the male maintains the same harem for several breeding seasons, or where there is promiscuity but both sexes contribute equally to parental care, conditions for conflict are equivalent to monogamy.

Alleles↗
PubMed1978

Experimental cryopreservation and autotransplantation of parathyroid glands: technique and demonstration of function.

A canine model for cryopreservation and autotransplantation of parathyroid glands was developed as a prototype for cryopreservation of human parathyroid glands; Each of 18 dogs had two parathyroids removed, sectioned, and cooled at a controlled rate to -80 degrees in media containing 10% dimethylsulfoxide and 10% autologous serum. After storage for two months at -196 degrees the tissue was thawed and implanted in muscle; the remaining two parathyroid glands were removed from the neck. Function was assessed by monitoring serum calcium levels and measuring parathyroid hormone levels in venous effluent from the graft beds. Autograft function was demonstrated in ten of 18 dogs; graft failure occurred in four dogs. In the remaining four dogs, function could not be evaluated because of accessory parathyroid tissue. Parathyroid tissue cryopreserved for nine months was documented to function in six of seven dogs. Histologic study of the cryopreserved, autografted tissue showed normal parathyroid architecture.

Animals↗