Observations on the thermal conductance of Adélie (Pygoscelis adeliae) and Humboldt (Spheniscus humboldti) penguins

 Analyses of cooling rates in one Adélie and one Humboldt penguin yielded calculated thermal conductance values of 0.1040 and 0.1672 W(kg ^°C)^-1, respectively. We review the methods used to calculate penguin surface area, an important component in calculating conductance values, and suggest that, in comparative studies of thermal balance, the use of body mass is a better estimator of body size than surface area. Using previously published data on penguin species, we found a significant model to predict thermal conductance from body mass according to: log C= log 0.1083−0.474 log M, where C is minimal specific thermal conductance in W(kg ^°C)^-1 and M is body mass in kilograms. Received: 13 June 1995/Accepted: 11 March 1996     

Allosteric effects of monoclonal antibodies on human growth hormone

We have previously shown that a monoclonal antibody (MAb) recognizing the human growth hormone (hGH) antigenic domain left exposed after binding to lactogenic receptors enhanced hGH binding probably through allosteric effects on the hormone binding site. Since receptors displaying different specificities would not recognize exactly the same hGH region, we explored whether some of our MAb could affect hGH binding to somatogenic receptors from rabbit liver and to human liver hGH-specific receptors.The effect of MAbAE5, AC8 and F11 on hGH binding was measured by determining the formation of¹²⁵I-MAb:hGH:receptor complexes using two different experimental approaches. Results from procedure A, which involved the previous binding of the hormone to microsomes before adding¹²⁵I-MAb, indicated that the hGH domain defined by epitopes AE5, AC8 and F11 is uncovered in the various hormone:receptor complexes.Procedure B was devised to reveal any alteration in the hGH molecule induced by the MAb. In this case preformed¹²⁵I-MAb:hGH complexes were added to microsomes. Data showed that¹²⁵I-MAb AE5:hGH complexes bound better to the various receptors than¹²⁵I-MAb AE5 to hGH:receptor complexes. On the contrary, hGH previously bound to¹²⁵I-MAb AC8 or¹²⁵I-MAb F11 was less recognized by the receptors than the free hormone. Furthermore, binding of MAb AE5 or MAb F11 to hGH 20 K (a natural hGH variant lacking residues 32–46) also enhanced its affinity to the various receptors whereas MAb AC8 did not inhibit hGH 20 K binding.Results indicated that MAb recognizing the hGH antigenic area that remains unmasked after binding to different membrane-bound receptors are able to affect hormone binding site. MAb would induce either positive or negative allosteric changes in the hormone region involved in its binding to lactogenic, somatogenic and hGH-specific receptors.     

Use of F1 progeny of HolsteinxZebu cross cattle as oocyte donors for in vitro embryo production and gene microinjection

This study was designed to determine the possibility of using F1 crossbreed cattle (Holstein x Zebu) as donors of oocytes for in vitro fertilization (IVF) and for pronuclear gene microinjection into in vitro-produced embryos. In the first part of the experiment oocytes from Bos taurus (Holstein), Bos indicus (Zebu) and F1 crossbred Bos taurus x Bos indicus (Holstein x Zebu) genotypes were inseminated with Bos taurus (Holstein) semen and were allocated for in vitro embryo production using conventional IVF procedures. No differences were observed on the in vitro maturation (IVM) rates between breeds (Holstein x Holstein:85%, Zebu x Holstein:84% and Zebu x Holstein x Holstein:88%). Holstein cows yielded the highest number of cumulus oocyte complexes (6.8 per ovary) for in vitro maturation, differing (P<0.05) from Zebu x Holstein and Zebu x Holstein x Holstein F1 by 5.1 and 5.8, respectively. However, the Holstein breed also yielded the lowest percentage of cleavage (45.1 vs 71.9% for Zebu x Holstein and 65.1% for Zebu x Holstein x Holstein). Of the 3 genotypes, the hybrid F1 breed was the most efficient source of oocytes for the production of embryos capable of reaching morulae and blastocyst stages (76 250 ; P< 0.001). In the second part of the study, 599 oocytes from the F1 breed were fertilized in vitro, 1 group of 150 oocytes was used for the determination of the optimal pronuclear visualization period. The highest number of oocytes with 2 pronuclei was observed between 24 to 28 h after IVF (27 to 42%). The remaining 399 oocytes were microinjected with a gene construct bearing the bacterial lacZ gene as the reporter for gene expression. Survival of embryos to microinjection was 73.8%, and 45.5% of them (50 110 ) cleaved in culture. Of the microinjected embryos, 1 out of 50 showed beta-galactosidase activity. These findings indicate that a tropical crossbreed of cattle (Zebu x Holstein x Holstein) can be used as a source of oocytes for IVF programs and gene microinjection studies.     

Damage to living trees contributes to almost half of the biomass losses in tropical forests

Accurate estimates of forest biomass stocks and fluxes are needed to quantify global carbon budgets and assess the response of forests to climate change. However, most forest inventories consider tree mortality as the only aboveground biomass (AGB) loss without accounting for losses via damage to living trees: branchfall, trunk breakage, and wood decay. Here, we use ~151,000 annual records of tree survival and structural completeness to compare AGB loss via damage to living trees to total AGB loss (mortality + damage) in seven tropical forests widely distributed across environmental conditions. We find that 42% (3.62 Mg ha⁻¹ year⁻¹; 95% confidence interval [CI] 2.36–5.25) of total AGB loss (8.72 Mg ha⁻¹ year⁻¹; CI 5.57–12.86) is due to damage to living trees. Total AGB loss was highly variable among forests, but these differences were mainly caused by site variability in damage-related AGB losses rather than by mortality-related AGB losses. We show that conventional forest inventories overestimate stand-level AGB stocks by 4% (1%–17% range across forests) because assume structurally complete trees, underestimate total AGB loss by 29% (6%–57% range across forests) due to overlooked damage-related AGB losses, and overestimate AGB loss via mortality by 22% (7%–80% range across forests) because of the assumption that trees are undamaged before dying. Our results indicate that forest carbon fluxes are higher than previously thought. Damage on living trees is an underappreciated component of the forest carbon cycle that is likely to become even more important as the frequency and severity of forest disturbances increase.     

Effect of different doses of chromium picolinate on protein metabolism in infant rats.

This 12-day study was conducted to evaluate the effects of three different levels of dietary chromium (100, 200, and 500 microg/day) in the form of chromium picolinate (CrPic) on growth and protein use in weaned rats. No significant effect of CrPic on body weight gain, food intake, or food conversion rate was observed. Elevated doses of CrPic seemed to increase muscle mass, either by stimulating protein anabolism by activation of insulin by chromium or by lowering protein degradation. However, these effects had no repercussions on overall growth, suggesting that any anabolic effect of chromium due to the action of insulin was probably marginal.     

The pattern of testosterone replacement influences the recovery of the stimulatory effect of clonidine on growth hormone (GH) secretion in orchidectomized rats

It has previously been described that the growth hormone (GH) releasing effect of clonidine (CLO), an agonist of ₂-adrenoreceptors, disappears after orchidectomy and is restored by testosterone replacement when started immediately after orchidectomy. In the present experiments, the effects of CLO on GH release was analysed in long-term (LTO; 12 weeks) and short-term (STO; 2 weeks) orchidectomized rats. In the first experiment, LTO males were implanted with silastic capsules containing testosterone 10 weeks after orchidectomy and killed 2 weeks later, 15 min after injection of CLO (150 μg/kg) or vehicle. In the second experiment, adult males were implanted with testosterone at the moment of orchidectomy and decapitated 2 or 12 weeks later, 15 min after vehicle or CLO administration. In addition, in order to evaluate the effects of orchidectomy and androgen replacement on ₂ agonists GH release further, prepubertal males (21-days-old) implanted with testosterone or 5--androstane-3-, 17β diol (-diol) at the moment of orchidectomy were killed 2 weeks later, 15 min after ketamine-xylazine (an ₂ agonist) administration. Finally, 10-day-old males (orchidectomized 72 h before) were decapitated 15 min after CLO or vehicle administration. Our results show that: (a) LTO and STO abolished the stimulatory effect of clonidine on GH secretion; (b) orchidectomy also abolished the stimulatory effect of clonidine in neonatal rats and that of xylazine in prepubertal males; (c) testosterone implanted at the moment of orchidectomy prevented the loss of the CLO effect in LTO and STO, but testosterone-delayed administration in LTO was unable to restore the effectiveness of CLO inducing GH release. We conclude that orchidectomy at all ages tested abolishes GH secretion induced by ₂ agonists, which suggests that the functionality of -adrenergic receptors involved in the control of GH secretion is critically dependent on a permanent exposure to testosterone in males.