Robust Institutional Support and Collaboration Between Summer Training Programs in Cancer and Biomedicine Drive the Pivot to a Virtual Format in Response to the COVID Pandemic.

Summer internships serve important roles in training the next generation of biomedical researchers and healthcare providers through laboratory and clinical experiences that excite trainees about these fields and help them make informed decisions about career paths. The SARS-CoV-2 (COVID) pandemic and associated physical distancing restrictions precluded implementation of traditional in-person summer curricula and led to the cancellation of many internships across the USA. COVID-related disruptions also created opportunities for trainees to engage in remote research, become proficient in online learning platforms, and explore multidisciplinary topics. These skills are highly relevant to trainees as virtual interfaces occupy an increasingly mainstream role in their professional paths. The response to the COVID pandemic required real-time adaptations at all levels for major biomedical institutions including the University of Maryland Baltimore (UMB). Pivoting summer programs to a virtual format as part of this response provided a "teachable moment" to expose trainees to the innovation and resilience that are essential components of the biomedical profession. UMB summer programs, which span diverse biomedical disciplines from cancer research to diabetes, consolidated resources and identified mentors with online research projects to develop a robust virtual curriculum. Herein, data from a cancer-focused internship illustrate the collaborative adaptations to established components and creation of new learning modules in the transition to, and implementation of, online training. Outcomes are presented in the context of the COVID pandemic and significant societal issues that arose in the summer of 2020. The utility of virtual components and their impact on future programs is discussed.

MUC5AC interactions with integrin ß4 enhances the migration of lung cancer cells through FAK signaling.

MUC5AC is a secretory mucin aberrantly expressed in various cancers. In lung cancer, MUC5AC is overexpressed in both primary and metastatic lesions; however, its functional role is not well understood. The present study was aimed at evaluating mechanistic role of MUC5AC on metastasis of lung cancer cells. Clinically, the overexpression of MUC5AC was observed in lung cancer patient tissues and was associated with poor survival. In addition, the overexpression of Muc5ac was also observed in genetically engineered mouse lung adenocarcinoma tissues (Kras(G12D); Trp53(R172H/+); AdCre) in comparison with normal lung tissues. Our functional studies showed that MUC5AC knockdown resulted in significantly decreased migration in two lung cancer cell lines (A549 and H1437) as compared with scramble cells. Expression of integrins (α5, ß1, ß3, ß4 and ß5) was decreased in MUC5AC knockdown cells. As both integrins and MUC5AC have a von Willebrand factor domain, we assessed for possible interaction of MUC5AC and integrins in lung cancer cells. MUC5AC strongly interacted only with integrin ß4. The co-localization of MUC5AC and integrin ß4 was observed both in A549 lung cancer cells as well as genetically engineered mouse adenocarcinoma tissues. Activated integrins recruit focal adhesion kinase (FAK) that mediates metastatic downstream signaling pathways. Phosphorylation of FAK (Y397) was decreased in MUC5AC knockdown cells. MUC5AC/integrin ß4/FAK-mediated lung cancer cell migration was confirmed through experiments utilizing a phosphorylation (Y397)-specific FAK inhibitor. In conclusion, overexpression of MUC5AC is a poor prognostic marker in lung cancer. MUC5AC interacts with integrin ß4 that mediates phosphorylation of FAK at Y397 leading to lung cancer cell migration.

Life and death decisions in B1 lymphoma cells.

Crosslinking of surface immunoglobulin (Ig) receptors with anti-IgM (anti-mu) but not anti-IgD (anti-delta) antibodies causes growth arrest and apoptosis in several extensively characterized B1-like lymphoma cell lines. While anti-mu stimulates a transient increase in c-myc mRNA and protein expression, followed by a rapid decline below the baseline level, anti-delta only causes a moderate increase in the expression of this oncogene, which returns to baseline levels within 24-48 hours. However, signals downstream from anti-delta can be converted into an apoptotic pathway by modulating PI3K activity, suggesting that PI3K is a critical rheostat controlling survival signals in B1 cell lines. Anti-mu-induced down-regulation of c-Myc is followed in time with an increase in the cyclin dependent kinase inhibitor, p27Kip1, in all anti-mu sensitive lymphoma lines. This increase correlates with growth arrest and apoptosis. The anti-mu-mediated decrease in c-Myc, increase in p27Kip1, growth arrest and apoptosis, can all be prevented via CD40/CD40L signaling. Inhibition of caspase activation, on the other hand, prevents anti-mu-induced apoptosis, but has no effect on c-Myc, p27Kip1, and G1 arrest. Interestingly, we also found that steroids and retinoids can mimic anti-mu-mediated signaling and lead to a loss of c-Myc, an increase in p27Kip1, G1 arrest, and apoptosis. Together, these data suggest that modulation of c-Myc and p27Kip1 protein levels is crucial for the life versus death decisions in murine immature B1-like lymphoma cells lines.

Cellular adaptations in fat tissue of exercise-trained miniature swine: role of excess energy intake.

This study examined the influence of energy expenditure and energy intake on cellular mechanisms regulating adipose tissue metabolism. Twenty-four swine were assigned to restricted-fed sedentary, restricted-fed exercise-trained, full-fed sedentary, or full-fed exercise-trained groups. After 3 mo of treatment, adipocytes were isolated and adipocyte size, adenosine A(1) receptor characteristics, and lipolytic sensitivity were measured. Swine were infused with epinephrine during which adipose tissue extracellular adenosine, plasma fatty acids, and plasma glycerol were measured. Results revealed that adipocytes isolated from restricted-fed exercised swine had a smaller diameter, a lower number of A(1) receptors, and a greater sensitivity to lipolytic stimulation, compared with adipocytes from full-fed exercised swine. Extracellular adenosine levels were transiently increased on infusion of epinephrine in adipose tissue of restricted-fed exercised but not full-fed exercised swine. These results suggest a role for adenosine in explaining the discrepancy between in vitro and in vivo lipolysis findings and underscore the notion that excess energy intake dampens the lipolytic sensitivity of adipocytes to beta-agonists and adenosine, even if accompanied by exercise training.

The swine as a model for studying exercise-induced changes in lipid metabolism.

The swine has many similarities to humans, making it an excellent research model in which to study the role of exercise on lipid metabolism. Swine adapt to exercise-training by increasing muscle oxidative enzymes, maximal stroke volume, cardiac output, VO2max, and high density lipoprotein cholesterol levels, while decreasing total cholesterol levels and resting heart rate. The lipoprotein profile of swine and humans is also similar, and low density lipoprotein is the major cholesterol transporting lipoprotein in both species. Several studies in swine report conflicting results on the effect of exercise-training on lipoprotein profile and atherosclerotic lesion appearance. This may result from differences in total exercise time between the studies. With sufficient total exercise, atherosclerosis was reduced and high density lipoprotein cholesterol levels were increased. Exercise may also play a role in reducing obesity, a risk factor for cardiovascular disease, by enhancing lipid mobilization from adipocytes. Recent research suggests that swine adipocyte sensitivity to adenosine, a locally-produced antilipolytic agent, is reduced after exercise treatment. Cellular mechanisms responsible for this metabolic change include a reduction in adenosine A1 receptor number. Current studies are examining the transport of extracellular cyclic AMP from adipocytes and its role as a potential adenosine precursor.

Does exercise intensity or diet influence lactic acid accumulation in breast milk?

PURPOSE: This study examined the relationships among diet, exercise intensity, and breast milk composition in lactating women. METHODS: Twelve lactating women were randomly assigned to either a high (N = 6; 5.03 g carbohydrate (CHO) x kg body mass (BM)(-1)) or moderate (N = 6; 3.89 g CHO x kg BM(-1)) carbohydrate diet. Milk and blood samples were collected before and after a nonexercise session (control) and maximal, lactic acid-threshold (LAT), and 20% below the LAT (LAT-20) intensities. RESULTS: The 30-min exercise LAT bout was more stressful than the 30-min LAT-20 bout (rating of perceived exertion (RPE) = 15 vs 12, respectively, P < 0.05). Milk LA was significantly higher at 0 min following maximal exercise in the high and moderate CHO groups (1.27+/-0.56 and 1.52+/-0.49 mM, respectively) and following LAT exercise (0.19+/-0.16 and 0.25+/-0.12 mM, respectively), when compared with the control session (0.08+/-0.03 and 0.09+/-0.05 mM, respectively). This was not observed following the LAT-20 exercise in the high and moderate CHO groups (0.11+/-0.04 and 0.12+/-0.08 mM, respectively). Elevated milk LA persisted in the 30-min collection point after maximal exercise only. There was no significant effect of dietary treatment on milk or blood LA at any of the collection points. CONCLUSIONS: In lactating women whose caloric needs are being met: 1) dietary CHO intake, within a practical range, does not influence LA levels in breast milk at rest or after exercise; 2) LA appearance in the milk is a function of exercise intensity; and 3) moderate intensity exercise (RPE = 12) will not increase breast milk LA levels.

Cyclic AMP metabolism by swine adipocyte microsomal and plasma membranes.

Extracellular cyclic AMP is source of extracellular adenosine in brain and kidney. Whether this occurs in adipose tissue is unknown. The present study evaluated the capacity of swine adipocyte plasma membranes to metabolize cyclic AMP to AMP and adenosine, via phosphodiesterase (PDE) and 5'-nucleotidase (5'-NT), respectively. Plasma membranes (PM) and microsomal membranes (MM) were isolated from over-the-shoulder subcutaneous adipose tissue of 3 month-old male miniature swine. The purity of the membrane fractions was determined and PDE and 5'-NT activities in PM and MM fractions were corrected for cross-contamination. The maximal activity of MM-PDE was 7-fold greater than that of PM-PDE. MM-PDE was 100% inhibited by 5 microM cilostamide, while PM-PDE was unaffected by this PDE3B inhibitor. Inhibitors of PDE1, PDE2, PDE4 and PDE5 also failed to inhibit PM-PDE. However, 1 mM DPSPX inhibited PM-PDE activity by 72%. When PM were incubated with 0.8 microM cyclic AMP for 20 min, AMP accumulation was four times that of adenosine. These data demonstrate that cyclic AMP can be converted to AMP and adenosine by the PM-bound enzymes 5'-NT and PDE, and suggest that the PM-PDE responsible for extracellular cyclic AMP metabolism to AMP is distinct from the intracellular MM-PDE.

Characterization of the swine adipocyte A1 adenosine receptor using an optimized assay system.

The radioligand binding assay of A1 adenosine receptors in adipocyte crude plasma membrane from Yucatan miniature swine was optimized by evaluating 17 factors involved in the assay. Significant effects of CHAPS, adenosine deaminase, EDTA, pre-rinsing glass fiber filters and pH were found for the binding measurements. Using the optimized procedure, [3H]8-cyclopentyl-1,3-dipropylxanthine, ([3H]-DPCPX) binding to A1 adenosine receptors in swine subcutaneous adipocyte crude plasma membrane was measured; Bmax and Kd values were 479 +/- 77 fmol/mg protein and 0.87 +/- 0.10 nM, respectively. Values for mesenteric adipose tissue from sedentary swine and subcutaneous adipose tissue from exercise-trained swine were also measured.

Mechanisms regulating adipocyte lipolysis.

Mechanisms regulating adipocyte lipolysis are reviewed in three stages. The first stage examines plasma membrane hormone receptors and G-proteins. The primary regulators of adipose tissue lipolysis, the catecholamines, bind to the alpha 2, beta 1, beta 2, and beta 3 adrenergic receptors. The alpha 2 receptor couples with Gi-proteins to inhibit cyclic AMP formation and lipolysis, while the beta receptors couple with Gs-proteins to stimulate cyclic AMP formation and lipolysis. The beta 1 receptor may mediate low level catecholamine stimulation, while the beta 3 receptor, which is activated by higher levels of catecholamines, may deliver a more sustained signal. The second stage examines the regulation of cyclic AMP, the intracellular messenger that activates protein kinase A. Adenylyl cyclase synthesizes cyclic AMP from ATP and is regulated by the G-proteins. Phosphodiesterase 3B hydrolyzes cyclic AMP to AMP and is activated and phosphorylated by both insulin and the catecholamines norepinephrine and epinephrine. The third stage focuses on the rate-limiting enzyme of lipolysis, hormone-sensitive lipase (HSL). This 82 to 88 kDa protein is regulated by reversible phosphorylation. Protein kinase A activates and phosphorylates the enzyme at 2 sites, and 3 phosphatases have been implicated in HSL dephosphorylation. The translocation of HSL from the cytosol to the lipid droplet in response to lipolytic stimulation may be facilitated by a family of lipid-associated droplets called perilipins that are heavily phosphorylated by protein kinase A and dephosphorylated by insulin. As the mechanisms regulating adipocyte lipolysis continue to be uncovered, we look forward to the challenges of integrating these findings with research at the in situ and in vivo levels.

Effect of bovine somatotropin and food deprivation on beta-adrenergic and A1 adenosine receptor binding in adipose tissue of lactating cows.

Lactating Holstein cows were used to assess the effect of bovine somatotropin (bST; n = 8) and fasting (FAST; n = 4) on ligand binding to beta-adrenergic (BAR) and Type-1 adenosine (A1R) receptors in adipose tissue. Cows received exogenous bST (sometribove; 40 mg/d) or no hormone (control) for 4 d in a single-reversal design with a 7-d interval between treatment periods. Subcutaneous adipose tissue biopsies were taken on day 4 of each treatment. Eight d after the bST regimen, 4 cows were fasted for 3 d and adipose biopsies were taken. Ligand binding was quantified with a postnuclear, total adipose tissue membrane preparation (100,000 x g pellet). Binding to BAR and A1R was assessed with the antagonists [125I]iodocyanopindolol (ICP) and [3H]8-cyclopentyl-1,3-dipropylxanthine (DCPCX), respectively. The binding affinity (Kd) of BAR for ICP was not affected by bST but was enhanced by FAST; maximal binding (Bmax) was increased with bST treatment (P < 0.06) and reduced by FAST (61%, P < 0.01). Kd values for DCPCX binding to A1R were not changed by bST or FAST. bST did not affect Bmax for A1R; however, FAST reduced the Bmax by 38%. Data highlight the differential regulation of BAR and A1R by bST and FAST.

Technical note: adipose tissue blood flow in miniature swine (Sus scrofa) using the 133xenon washout technique.

The purpose of this study was to examine the 133xenon washout technique as a viable method for measuring adipose tissue blood flow (ATBF) in swine. Using a total of 32 female Yucatan miniature swine (Sus scrofa), the partition coefficient for 133xenon in swine subcutaneous adipose tissue was determined and ATBF was measured at rest and under various physiological conditions. These conditions included feeding, anesthesia, epinephrine infusion, and acute exercise. The effects of epinephrine and acute exercise were examined in both sedentary and exercise-trained swine. The partition coefficient value for 133xenon in swine subcutaneous adipose tissue was 9.23+/-0.26 mL/g (mean +/- SD, n = 10). The average value for resting ATBF in swine was 3.98+/-2.72 mL/(100 g tissue-min) (n = 19). Feeding increased ATBF by approximately fivefold over fasting values, and isoflurane anesthesia significantly decreased ATBF compared to rest (1.64+/-1.12 vs 3.92+/-4.22 mL/[100 g x min], n = 10). A 30-min epinephrine infusion (1 microg/[kg BW x min]) significantly increased ATBF from a resting value of 3.13+/-2.61 to 10.35+/-5.31 mL/(100 g x min) (n = 12). Epinephrine infusion into exercise-trained swine increased ATBF to the same extent as when infused into sedentary swine. An acute, 20-min bout of exercise significantly increased ATBF in swine, and the sedentary swine showed a larger increase in ATBF than their exercise-trained littermates relative to rest: 7.83 vs 2.98 mL/(100 g x min). In conclusion, the 133xenon washout technique appears to be a viable method for measuring ATBF in swine; our findings are comparable to swine ATBF values reported using the microsphere method and are consistent with values reported in animal and human studies.

Adipose tissue beta-adrenergic and A1 adenosine receptors in suckling pigs.

During the first few weeks after birth, major changes occur in porcine adipocyte lipid metabolism. Two of the important receptors controlling lipid metabolism in adipocytes are the beta-adrenergic receptors (betaAR) and the A1 adenosine receptors (A1R). To gain insight into the role of these receptors in modulating neonatal adipocyte lipid metabolism, we measured receptor affinity and number in suckling pigs. Adipose tissue from crossbred (X-Bred) and genetically obese suckling pigs at 0, 3, 10, and 17 d of age was used to prepare crude membranes. The betaAR and A1R number and affinity were measured in membranes by equilibrium saturation binding with radioligands. Obese pigs were smaller than X-Bred pigs (average weight = 1.62 and 2.43 kg for obese and X-Bred, respectively; P < .01). Osmium-fixed adipocytes were larger in obese pigs than in X-Bred pigs (average cell diameter = 34.4 and 30.1 microm for obese and X-Bred, respectively; P < .01). In the obese and X-Bred pigs, the affinity of the betaAR for iodocyanopindolol was greater (lower Kd) at 17 d than at the younger ages (average Kd = 177 pM at 17 d compared with > 330 pM at younger ages; age effect P < .01). The pattern for the betaAR number was complex; the lowest receptor number was at 10 d of age in obese and X-Bred pigs (average number = 41 at 10 d compared with > 65 fmol/mg protein at older and younger ages; age effect P = .03). The higher betaAR Kd and the lower receptor number in younger animals suggest less regulation by physiologic concentrations of epinephrine and norepinephrine. This would allow greater anabolic lipid metabolism to proceed during the neonatal period, when adipocytes increase four- to sixfold in volume. There were no measurable A1R at any of these early ages; thus, adenosine control mechanisms to counteract the betaAR and provide negative controls to lipid accretion are not operable in suckling pigs.

Influence of nutritional weaning on porcine adipocyte beta-adrenergic and adenosine A1 receptors.

Obese and crossbred (X-Bred) pigs were removed from sows at 14 d of age and given ad libitum access to a high-fat, milk-based diet. A subset of pigs fed this diet were killed at 28 and 49 d of age. At 28 d, another subset of pigs was given ad libitum access to a low-fat, grain-based diet and were killed at 31, 35, and 49 d of age (nutritionally weaned for 3, 7, and 21 d, respectively). Dorsal subcutaneous adipose tissue was obtained at death and adipocytes were prepared by incubation with collagenase. A portion of the cells was fixed with osmium to determine size and number; remaining cells were lysed in hypotonic media and centrifuged to yield a crude membrane fraction. The beta-adrenergic receptor (beta-AR) and A1 adenosine receptor (A1R) affinity and number were measured in the membranes by equilibrium saturation ligand binding. Obese pigs had a lower body weight than X-Bred pigs at all ages (P < .05). Obese pigs tended (P for volume > .1 but < .2) to have larger adipocytes than X-Bred pigs. The beta-AR affinity did not differ between obese and X-Bred pigs. There were fewer beta-AR per milligram of membrane protein in obese than in X-Bred pigs at 28 and 49 d of age when fed the high-fat, milk-based diet (P < .01). However, beta-AR number expressed per cell or unit cell surface area did not differ between genetic groups. As pigs of either genetic group continued to be fed the low-fat, grain-based diet, the beta-AR decreased when expressed per milligram of protein or unit cell surface area (P < .05) and tended to decrease when expressed per cell. Obese and X-Bred pigs fed the high-fat, milk-based diet had more beta-AR than respective pigs fed the low-fat, grain-based diet when data were expressed per milligram of protein (P < .01) but not when expressed per cell or unit surface area. The A1R were only detectable in 2 of 16 X-Bred litters but were more developed in adipocytes of obese pigs, being measurable in 8 of 14 litters. The A1R number, expressed per milligram of protein, was lower in obese pigs fed the milk-based diet than in those fed the grain-based diet (P < .05). These findings suggest the decreased beta-AR number after nutritional weaning, or the transition from a high-fat to low-fat diet, may contribute to fat accretion in pigs. Furthermore, the lower number of beta-AR in obese than in X-Bred pigs may contribute to the obesity.

Breast milk composition after exercise of different intensities.

The purpose of this study was to determine if breast milk composition changed significantly following exercise conducted at different intensities. Nine postpartum women exercised on a treadmill up to maximal oxygen uptake (100% of VO2max) on the first laboratory visit, for 30 minutes on two subsequent occasions (50% and 75% of VO2max) and also performed a nonexercise control session. Blood and breast milk were collected prior to exercise, immediately after exercise, and at 30, 60, and 90 minutes postexercise. Blood samples were analyzed for lactic acid (LA) while milk samples were analyzed for LA, pH, lipid, ammonium, and urea. Milk LA after the 100% intensity session was significantly elevated through 90 minutes postexercise, while there was no significant increase in milk LA at any collection time after the 50% or 75% intensity sessions. There were no significant differences in milk pH, lipid, ammonium, or urea measurements after any of the exercise sessions. These data show that unlike maximum intensity exercise, moderate intensity exercise does not increase breast milk LA content.

Mice deficient in MIM expression are predisposed to lymphomagenesis.

Missing in metastasis (MIM) is a member of newly emerged inverse Bin-Amphiphysin-Rvs (BAR) domain protein family and a putative metastasis suppressor. Although reduced MIM expression has been associated with bladder, breast and gastric cancers, evidence for the role of MIM in tumor progression remains scarce and controversial. Herein we characterized a MIM knockout mouse strain and observed that MIM-deficient mice often developed enlarged spleens. Autopsy and histological analysis revealed that nearly 78% of MIM(-/-) mice developed tumors with features similar to diffuse large B lymphoma during a period from 1 to 2 years. MIM(-/-) mice also exhibited abnormal distribution of B cells in lymphoid organs with decrease in the spleen but increase in the bone marrow and the peripheral blood. Furthermore, the bone marrow of MIM(-/-) mice contained a higher percentage of pre-B2 cells but fewer immature B-cells than wild-type mice. In response to CXCL13, a B-cell chemokine released from splenic stromal cells, MIM-deficient B-cells did not undergo chemotaxis or morphological changes in response to the chemokine and also did not internalize CXCR5, the receptor of CXCL13. Microarray analyses demonstrated that MIM is the only member of the I-BAR domain family that was highly expressed in human B cells. However, low or absent MIM expression was common in either primary B-cell malignancies or established B-cell acute lymphocytic leukemia or lymphomas. Thus, our data demonstrate for the first time an important role for MIM in B-cell development and suggest that predisposition of MIM-null mice to lymphomagenesis may involve aberrant interactions between B lineage cells and the lymphoid microenvironment.

Stimulation of receptor-associated kinase, tyrosine kinase, and MAP kinase is required for prolactin-mediated macromolecular biosynthesis and mitogenesis in Nb2 lymphoma.

Lactogens [prolactin (Prl) and growth hormone] stimulate phosphorylation of the 40S ribosomal protein, S6, in Nb2 cells by mechanisms that do not involve participation of cAMP or protein kinase A, protein kinase C, or cGMP-dependent protein kinase. However, inhibition of tyrosine kinase (TK) abrogates Prl-mediated macromolecular biosynthesis. Inasmuch as lactogen signaling may involve sequential activation of protein kinases, the effect of Prl on the well-characterized mitogen-activated protein kinase (MAPK) and S6 kinase (S6K), the enzyme responsible for S6 phosphorylation in vivo, and their relationship to Nb2 macromolecular biosynthesis and mitogenesis were investigated. The results show that MAPK stimulation is transient (peak activity, 30 min) and precedes that of S6K, which reaches a maximum at 1.5-2 h, and slowly returns towards control levels at 6 h. Both staurosporine which inhibits GH receptor-associated kinase (JAK2) and genistein (GEN), an inhibitor of membrane-associated and cytoplasmic TKs, abrogate Prl-stimulated TK, MAPK, and S6K. Rapamycin (RAP), a specific inhibitor of p70S6K, completely blocks S6K but does not affect TK and MAPK. TK and MAPK activity correlates with Prl-stimulated anabolism, i.e., protein and DNA synthesis and mitogenesis. Thus, concentrations of STR and GEN which abrogate TK and MAPK inhibit anabolism virtually 100%. However, RAP, which inhibits S6K (ca. 100%) but not TK or MAPK, only delays Prl-mediated anabolism. These results indicate that Prl signaling in Nb2 cells involves a protein kinase cascade and that regulation of receptor-associated kinase, TK, and MAPK correlates with anabolism. The role of S6K (and S6 phosphorylation) appears to be ancillary.

Exercise attenuates the anti-lipolytic effect of adenosine in adipocytes isolated from miniature swine.

Four pairs of female and six pairs of male litter-mate Yucatan miniature swine (Sus scrofa) were used in this study which examined the possibility that endurance exercise training reduces the sensitivity of adipocytes to the anti-lipolytic effects of adenosine. One member of each pair was exercise-trained on a treadmill for three months while its litter-mate remained sedentary, after which time over-the-shoulder fat and left brachialis muscle were biopsied. Despite a predominance of type IIB fibres, biopsied muscle of exercised swine had 38% more citrate synthase activity than controls (P < 0.05). The average cell diameters of adipocytes isolated from exercisers were 14% smaller (P < 0.05) than those from controls. Rates of adrenaline-stimulated lipolysis expressed as nmol glycerol released/90 min incubation period per 10,000 cells failed to differ between the two groups; however, when expressed per cm2 surface area, a significant 37% increase was observed. Incubation with 1 microM adrenaline and increasing doses of phenylisopropyladenosine (PIA) caused a rightward shift in the dose-response curve of adipocytes in five of the ten exercisers compared to litter-mate controls. The concentration of PIA causing one-half inhibition of lipolysis was 64% greater in adipocytes from exercisers than controls (4.03 nM vs. 2.49 nM, n = 10, P < 0.05). These data support the hypothesis that endurance exercise-training induces a reduction in adipocyte sensitivity to adenosine, thereby facilitating fatty acid mobilization.

Dietary fat saturation and endurance exercise alter lipolytic sensitivity of adipocytes isolated from Yucatan miniature swine.

This study examined the effects of dietary fat saturation and endurance exercise on lipolytic sensitivity of adipocytes isolated from Yucatan miniature swine. Twenty-four female swine had free access to a high fat diet with a polyunsaturated to saturated fat ratio (P:S) of 0.3 or 1.0, and were treadmill-exercised or remained sedentary. After 3 months, biopsies were taken, adipocytes were isolated and lipolytic activity was determined. Adipocytes were incubated with adenosine deaminase followed by epinephrine, isoproterenol, or epinephrine plus phenylisopropyladenosine, and glycerol release was measured. Backfat thickness was measured by ultrasonography. Our findings revealed that 1) adipocytes from 1.0 P:S diet-fed swine released 30% more glycerol than adipocytes from 0.3 P:S diet-fed swine when stimulated by 1 micromol/L isoproterenol; 2) adipocytes from exercised swine released 45% more glycerol than adipocytes from sedentary swine when stimulated by 1 micromol/L epinephrine; 3) body weight of exercised swine was significantly lower than sedentary swine; and 4) backfat thickness was less in exercised swine than in sedentary swine (2.39 vs. 2.95 cm, P = 0.002). We conclude that ad libitum consumption of diet with a P:S of 1.0, combined with endurance exercise, increases lipolytic sensitivity, lowers body weight gain, and reduces fat accumulation in female Yucatan miniature swine.