Endocrine profiles during doe-litter separation and the subsequent pregnancy in rabbits

This study was carried out to determine the effects of a transient doe-litter separation on plasma prolactin, LH, FSH, estradiol-17beta and progesterone concentrations before artificial insemination and during the subsequent pregnancy. Control does (n=12) had free access to nursing, whereas separated does (n=12) were kept away from their litters for 48 hours before artificial insemination. Both groups were inseminated on day 11 after parturition. Teat stimulation by suckling caused a high increase in prolactin concentrations in separated does (p < 0.0001). Basal prolactin concentrations were observed in both groups on days 8 and 18 of pregnancy. No effect of the treatment was detected on LH and FSH concentrations during the sampling period. A rise of estradiol-17beta concentrations was observed 48 hours after doe-litter separation, compared to control does and to previous values (p < 0.003). Both groups showed low progesterone concentrations before artificial insemination. Pregnant rabbits in both groups showed increased progesterone concentrations on days 8 and 18 of pregnancy. Lower estradiol-17beta concentrations were observed in control does on day 18 of pregnancy compared with separated rabbits (p < 0.003). The results suggest that a transient separation of nursing does from their litters before artificial insemination may promote high follicular steroidogenesis activity leading to increased estradiol-17beta concentrations. This hormonal change could be a result of several stimulatory actions probably triggered by the absence of suckling episodes and may affect the luteotrophic function during the subsequent pregnancy.     

Comparison of embryo recovery, embryo quality, oestradiol-17 beta and progesterone profiles in domestic cats (Felis catus) at natural or induced oestrus

Domestic cats experiencing a natural or FSH-induced oestrus were studied. Mated cats produced fewer (P less than 0.01) unfertilized oocytes and more (P less than 0.01) morulato blastocyst-stage embryos of better quality after a natural oestrus than after FSH treatment. Serum oestradiol-17 beta concentrations were lower (P less than 0.05) and progesterone levels rose earlier (P less than 0.05) in the induced oestrus compared to the natural oestrus group. Morula/blastocyst-stage embryos from both groups transferred to 15FSH/hCG-treated recipients produced 3 pregnancies and 2 live-born litters (1 from a natural oestrus donor and 1 from an FSH-treated donor). These results indicate that fertilization rates and embryo quality in domestic cats appear to be compromised by the FSH treatment, probably because of altered oestradiol-17 beta and progesterone concentrations.     

OPTIMUM BROOD SIZE: TESTS OF ALTERNATIVE HYPOTHESES

The most productive litter size (five) was not as common as expected in a free-living population of white-footed mice. I evaluated four competing hypotheses that can explain this pattern. Reproductive costs and annual variation in recruitment appear to be insufficient explanations for the empirical distribution of litter size. Optimal investment of reproductive resources that vary among parents is supported by some tests, but not by all. The abundance of litters less than the apparent optimum is at least partially explained by asymmetric survival in large litters (the cliff-edge hypothesis). Hypotheses that explain the empirical distribution of brood size are not mutually exclusive. Several mechanisms can act alone, or interact, to create an average brood size less than that which appears to produce the greatest number of descendants.     

Hemorrhagic necrosis of the central nervous system of fetal hamsters: litter incidence and age-related pathological changes

The occurrence, anatomic distribution, and character of lesions of spontaneous hemorrhagic necrosis (SHN) are reported in each hamster fetus of two affected litters examined on the fifteenth day of gestation and in selected individuals of other affected litters on the twelfth, thirteenth, and fourteenth days of gestation. The pathologic process seems primarily to affect the capillary vasculature of the central nervous system and shows a predilection for rapidly growing and differentiating regions of the fetal forebrain, thalamus, and brain stem. Lesions demonstrable in members of affected litters of susceptible stocks are of a progressive character, increasing both in severity and topographic extend with increasing fetal age and growth. Spontaneous patterns of regression and recurrence of SHN disease in susceptible stocks may reflect variable physiologic factors in the intrauterine environment.     

三江平原小叶章湿地枯落物初期分解动态

通过4周淋洗分解试验,探讨了微生物活动和淋洗作用对三江平原沼泽湿地沼泽化草甸小叶章和湿草甸小叶章枯落物初期分解的影响.结果表明：两种小叶章植物初期分解的质量损失分别占当年分解物质损失量的59％和22％,28 d分解后枯落物残留量明显降低,并呈先快后慢的变化过程.两种枯落物中N、P含量均有明显下降,N含量分别下降了约3265%和2455%,P下降了36.71%和45.15％.抑制微生物处理的枯落物N、P含量较不抑制处理高,但差异不显著;抑制和不抑制微生物处理下枯落物释放到淋洗液N、P含量变化也不相同,但差异未达到显著水平.表明小叶章初期分解主要受淋洗作用的影响.两种小叶章植物的分解速率和养分损失速率差异均未达到显著水平.     

Birth weight variation in the domestic pig: effects on offspring survival, weight gain and suckling behaviour

In domestic pigs, litter-mates often vary considerably in birth weight. To examine whether this size variation influences piglet survival, weight gain and suckling behaviour, we experimentally manipulated the number and size distribution of litter-mates in 51 litters. Litters were small (eight or nine piglets) or large (11 or 12 piglets) compared to the herd mean of 10 piglets, and were made more or less variable in weight by using the largest and smallest quartiles of two combined litters (variable) or the middle two quartiles (uniform). Weights were measured on days 0, 3 and 21. Behavioural measures (percent of nursings missed, mean teat consistency score, per capita number of teat disputes before milk ejection, and percent time spent in teat disputes in the 20min after milk ejection) were recorded on days 1, 4, 10 and 17. Piglet weight variation (percent of coefficient of variation, CV) almost doubled over the 21 days in uniform litters and actually decreased in variable litters, but still remained higher in the variable litters. Overall, survival, percent of nursings missed, consistency in piglets' use of teats, number of teat disputes, percent time a piglet spent in teat disputes after milk ejection, and weight gain were unaffected by birth weight variation although there was a tendency (P=0.09) for more piglet deaths in variable litters. Behavioural measures of sibling competition were higher in large litters. The data provide little support for the hypotheses that high birth weight variation results in decreased survival, or that it permits rapid establishment of dominance, thereby reducing wasteful competitive behaviour in surviving piglets.     

Adaptation of siblings of female rats given ethanol effect of N-acetyl-L-cysteine

Summary Ethanol administration to female rats before and during pregnancy resulted in decreased number of litters and increased activities of serum GOT, GPT and ALP. The hepatotoxicity of ethanol was indicated by the histological alterations both in the mother and siblings. There was increased levels of tissue lipids in mother and litters born to alcoholic rats. The concentration of TBARS in the liver and kidney were significantly increased in alcohol treated rats and their litters. The activities of the anti-peroxidative enzymes SOD and CAT were decreased on alcohol treatment in female rats. The glutathione content in liver and kidney decreased significantly in litters born to alcoholic rats.We have observed that the treatment with N-acetylcysteine offers protection against the toxic effect of alcohol in female rats during pregnancy and litters born to them. In N-acetylcysteine treated rats the number of litters as well as the average birth weight were close to that of control animals. Nacetylcysteine decreases the activities of serum GOT, GPT and ALP in female rats. We have also observed decreased levels of tissue lipids in mother and litters born to alcoholic rats given N-acetylcysteine when compared to alcoholic rats. The levels of TBARS in liver, kidney were also decreased both in mother and litter born to alcohol + N-acetylcysteine, while the activities of SOD and CAT were increased in liver of alcoholic rats given N-acetylcysteine when compared to alcoholic rats. Histopathological studies also showed the protective effect of N-acetylcysteine in both mother and litter in liver and kidney against alcoholic induced toxicity.     

闽江口互花米草淤积作用对其自身和短叶茳芏残体分解及硫养分释放的影响

2016—2017年,以闽江口鳝鱼滩西北部互花米草(SA)入侵初期与短叶茳芏(CM)形成的典型交错带植物残体为研究对象,基于野外原位分解试验,通过设定无淤积强度(S_0,0 cm/a)、当前淤积强度(S_5,5 cm/a)和未来淤积增强(S_(10),10 cm/a)3种处理,模拟互花米草入侵初期导致的淤积作用对其自身以及短叶茳芏残体分解及硫养分释放的影响。结果表明,随着互花米草入侵导致的淤积强度的增加,互花米草和短叶茳芏残体的分解速率均明显降低;与S_0相比,二者在S_5与S_(10)处理下的分解速率分别降低49.09%(SA)、35.14%(CM)和56.36%(SA)、44.59%(CM)。随着淤积强度的增加,互花米草和短叶茳芏残体分解过程中的TS含量整体均呈增加趋势,且其对短叶茳芏TS含量变化的影响较为明显;互花米草和短叶茳芏残体在分解过程中均表现为不同程度的硫释放,但随淤积强度的增加,二者硫释放量均呈降低趋势,且在相同淤积强度下,前者的硫释放量要高于后者。不同淤积强度下残体分解速率及硫养分释放强度的差异不仅与分解环境中的EC密切相关,且与残体残留率、初始基质质量(C/N和C/S)以及淤积导致养分条件改变而对分解过程中残体基质质量的影响有关。研究发现,随着淤积强度的增加,两种残体的分解速率及硫释放强度均降低;但在相同淤积强度下,短叶茳芏残体的分解速率和硫释放量均大于互花米草。     

Localization and expression of integrin subunits in the embryoid bodies of F9 teratocarcinoma cells

F9 embryonal carcinoma cells can differentiate in vitro into either parietal (PE) or visceral (VE) endoderm, depending upon specific retinoic acid (RA) treatment and growth conditions. In differentiated aggregates of F9 cells (EB), the VE is a polarized monolayer surrounding a core of undifferentiated cells. Within 7 days of treatment the cells organize their cytoskeleton and synthesize large amounts of extracellular matrix proteins to form a basal lamina under the newly formed epithelium. All these changes are likely to involve integrin expression and organization. In this study we have analyzed the spatio-temporal changes in the pattern and level of expression of beta1, beta4, alpha5, alpha6A, and alpha6B integrin subunits. We found that the organization of the VE monolayer in F9 aggregates involves both qualitative and quantitative changes in integrin expression. beta1 is downregulated and accumulates in the forming epithelium. The same occurs for alpha5, although its location on the surface of the aggregate appears to be transient as in fully differentiated EB its distribution is uniform. beta4 and alpha6A are also mainly localized in the VE but they are undetectable in undifferentiated aggregates and their expression is induced by RA treatment. An important exception is represented by alpha6B whose distribution and expression remain almost unchanged throughout treatment.     

Antisense suppression of GABA(A) receptor beta subunit levels in cultured cerebellar granule neurons demonstrates their importance in receptor expression

GABA(A) receptors in the CNS are pentameric molecules composed of alpha, beta, gamma, delta, epsilon and theta subunits. Studies on transfected cells have shown that GABA(A) receptor beta subunit isoforms can direct alpha1 subunit localization within the cell. To examine the role of selected subunits in governing GABA(A) receptor expression in neurons, cultures of rat cerebellar granule cells were grown with antisense or sense oligodeoxynucleotides (ODNs) specific for the alpha 1, beta 2 or gamma 2 subunits. These subunits are all expressed in granule neurons where they are thought to contribute to an abundant receptor type. Following ODN treatment, subunit expression and distribution were examined by western blotting, immunocytochemistry and RT-PCR. Treatment of the cultures with the antisense, but not the corresponding sense, ODNs reduced the levels of the targeted subunit polypeptides. In addition, the beta 2 antisense ODN reduced the level of the alpha1 subunit polypeptide without altering the level of its mRNA. In contrast, treatment with the beta 2 subunit antisense ODN did not alter gamma 2 subunit polypeptide expression, distribution or mRNA level. These findings suggest that the alpha1 subunit requires a beta subunit for assembly into GABA(A) receptors in cerebellar granule neurons.     

Differential growth patterns between successive litters of the eusocial Damaraland mole-rat, Cryptomys damarensis, from Namibia

Differential mean rates of growth were calculated for successive litters of mole-rats born to genetically unrelated pairs of C. damarensis. The Logistic equation provided the closest fit to the growth data.
Both intra- and inter-colonial variation in mean maximum growth rate between successive litters incorporated into the natal colonies were determined.
The mean asymptote (A), growth rate constant (K) and inflection time (I) were modelled for the first five litters of pups born to pairs of mole-rats. Inter-colonial analysis of recruitment to colonies revealed litters 1, 2, and 5 to grow faster than litters 3 and 4. Litters 1 and 2 had significantly higher asymptotes and inflection times than litters 3, 4, and 5 ( P < 0.001). All litters were assimilated into their natal colonies. There were no significant differences between males and females for the asymptote, growth rate constant, or inflection time ( P < 0.05).
Intra-colonial variation of litters 1 to 4 born to a single colony revealed comparable results to that obtained for inter-colonial comparisons. Multiple comparisons showed litters 1 and 2 to have a significantly higher absolute growth rate than litters 3 and 4. The lowest rate of growth being for litter 4.
The patterns of mean differential growth are discussed in the light of the social organization of the colony. It is postulated that growth rates in litters 1, 2, and 3 are more rigid since they constitute the main functional unit of colony organization. Litters 4 and 5 show a greater plasticity in growth; it is speculated that these colony members become incorporated into the various worker and defender groupings which are characteristic of C. damarensis colonies.     

Polyphasic growth-weight response in the guinea pig

An assessment of the growth rate pattern based on longitudinal weight data of guinea pigs was conducted over the presumptive preweaning and early postweaning period. The study covered the minimum of 44 and maximum of 53 days with means calculated for 3-day intervals involving 13 litters and a total of 40 young. Initial analysis showed males heavier than females at birth and both sexes being inversely proportional to litter size at birth. At the end of the experimental period the males were still heavier than the females but their weight distribution peaked in litter of three while the females were heaviest in the largest litters of five and lightest in the litter of one. Phasic linear regression line analysis revealed 4 litters with a triphasic growth outline and 6 litters with quadrophasic growth outline. Final assessments indicate that the total period of 53 days manifests a quadrophasic growth outline while, in contrast, the period specifically involved with the process of lactation and weaning displays a definite diphasic growth spectrum and is comparable to the tri- or quadrophasic spectrum occurring in the albino rats, rice rats and hamsters.     

氮-硫沉降对邓恩桉及杉木人工林凋落物C和N残留率的影响

采用二次正交回归旋转设计,以Na2S04为硫源、46％CO（NH2）2为氮源模拟氮一硫沉降,分析了不同氮一硫沉降水平下邓恩桉（Eucalyptus dunnii Maiden）和杉木[Cunninghamia lanceolata（Lamb．）Hook．]人工林凋落物中C和N残留率的动态变化,并采用Olson指数模型对c和N分解模型进行拟合。结果表明：在不同氮一硫沉降水平下,在1年内随处理时间延长邓恩桉和杉木凋落物的C和N残留率总体上均呈下降趋势;且N较难释放,总体表现为“释放一富集一释放”的动态过程;但在不同氮一硫沉降水平下及不同处理时间凋落物中C和N残留率均有极显著差异（P〈0．01）。凋落物中C和N分解的Olson指数模型的相关性总体上达到极显著或显著（P〈0．05）水平;邓恩桉和杉木凋落物中C和N的平均分解系数分别为0．877和0．208、0．704和0．600,平均周转期分别为3．148和15．877a,4．090和4．947a,显示凋落物中C释放速率大于N,杉木凋落物的C周转期大于邓恩桉但其N周转期则小于后者。在Na2SO4164kg·hm-1·a-1的水平下,氮沉降对邓恩桉凋落物的C和N释放及杉木凋落物的N释放有促进作用,但对杉木凋落物的C释放有抑制作用;在46％CO（NH：）：150或256kg·hm-2·a-1。的水平下,硫沉降也具有同样的作用。随分解时间的延长,邓恩桉凋落物的C／N值呈波动但总体减小的趋势,而杉木凋落物的C／N值呈波动趋势;但在不同氮一硫沉降水平下凋落物的C／N值均有极显著差异,且邓恩桉凋落物C／N值的变化幅度总体上大于杉木凋落物。     

The effects of open-air fumigation with sulphur dioxide on the decomposition of sycamore (Acer pseudoplatanus L.) leaf litters from polluted and unpolluted woodlands

Sycamore (Acer pseudoplatanus L.) leaf litters from 15 woodlands exposed to a broad range of ambient sulphur dioxide (SO₂) concentrations were fumigated with environmentally realistic concentrations (ll-20nmol mol^?1) of SO₂, for 166 d in an open-air fumigation experiment. Fumigation of the sycamore litters significantly increased sulphate-S and proton leaching, and decreased calcium, magnesium and potassium concentrations in leachates and leaf tissues. Leaf litters from relatively unpolluted woodlands showed a tendency to lose higher amounts of sulphate-S, calcium, magnesium and nitrate-N in leachates than litters from polluted sites when exposed to elevated levels of SO₂ in treatment plots. Fumigation inhibited the decomposition rates (CO₂ evolution) of the leaf litters. Marked changes in the composition of the saprotrophic fungal communities in SO₂-fumigated leaf litters were also recorded, but fungal communities and responses to SO₂, were similar between woodlands. There was no evidence from our data to suggest that resistance to SO₂, was developed in decomposer mycofloras in woodlands more frequently polluted by the gas.     

外源氮持续输入对相应氮梯度下碱蓬残体分解及硫养分释放的影响

以黄河口北部滨岸高潮滩的碱蓬残体为研究对象,将第一年度野外原位氮输入试验(N0:无额外氮处理;N1:低氮处理;N2:中氮处理;N3:高氮处理)获得的不同基质质量残体(NL0,NL1,NL2和NL3),原位投放至来源样区,并通过第二年度的持续输氮,探讨外源氮持续输入条件下残体基质质量改变对其分解速率和硫养分释放的影响。结果表明,随着氮输入量的增加,不同基质质量残体的分解速率整体表现为NL1NL3NL2NL0,说明外源氮持续输入条件下基质质量改变促进了残体的分解,且该促进作用在低氮处理下表现的最为明显,原因主要与其在残体分解过程中C/N比的改变程度最为明显有关。不同基质质量残体中的TS含量均呈不同程度波动变化特征,且其与相应的C/S比均呈相反规律变化,说明C/S比是调控不同氮持续输入条件下残体分解过程中硫含量变化的主控因素。不同基质质量残体的硫养分在分解期间均发生不同程度的净释放,且释放强度整体表现为NL3NL1NL2NL0,说明外源氮持续输入条件下残体基质质量改变促进了其硫养分释放,且该促进作用在高氮处理下表现的最为明显。研究发现,未来黄河口氮养分负荷增加的情况下,碱蓬残体的基质质量(C/N和C/S)将发生改变,而持续增强的氮负荷又会促进不同基质质量残体的硫养分归还,从而加速硫的生物循环速率。     

The development of white adipose tissue. Effect of litter size on the lipoprotein lipase activity of four adipose-tissue depots, serum immunoreactive insulin and tissue cellularity during the first year of life in male and female rats.

(1.) Male and female rats reared in litters of four gained body weight more rapidly than animals reared in litters of 16. The differences were more marked in males than females and became less marked in both sexes with advancing age. (2.) The relative weights of the perigenital, perirenal, subcutaneous and intramuscular white-adipose-tissue sites in the animals from small litters indicated their relative obesity compared with animals from large litters. A sex-related difference in the distribution of adipose tissue between the four sites was seen in animals reared in litters of both four and 16. (3.) Although at 30 days of age all the animals had more numerous and larger fat-cells in their white-adipose-tissue depots than animals reared in large litters, the pattern of change thereafter was both site- and sex-specific. During the post-weaning period (30-300 days), although detailed differences were apparent between sites, a general pattern of increased cell size in males and increased cell numbers in females emerged as being the important determinants responsible for the differences in depot sizes seen when animals from litters of four and 16 were compared. (4.) Lipoprotein lipase activities, expressed as units/g fresh wt. of tissue, in the depots of animals reared in groups of four were unaltered compared with those reared in groups of sixteen during the post-weaning period (47-300 days of age), and enzyme activities expressed per depot merely reflected differences in tissue weights. (5.) Lipoprotein lipase activities per 10(6) cells were higher in males reared in fours compared with those reared in sixteens of equivalent age, but were unaltered for females. (6.) The persistent hyperinsulinaemia of animals reared in litters of four is discussed in relation to the observed differences in enzyme activity and white-adipose-tissue cellularity.     

Control of variance in experimental studies of hyperlipidemia using the WHHL rabbit

Between-animal variability has frustrated many experimental studies in outbred animal models of human disease. Variability that arises from genetic heterozygosity can be minimized by use of experimental designs that match littermates (polyzygotic twins) across control and treatment groups. Poor breeding vigor has prevented use of this experimental design in the WHHL rabbit model of hyperlipidemia and atherosclerosis. A comparison of reproduction in WHHL and normal rabbits demonstrated that litter size is limited by functional deficits at ovulation, implantation, and gestation in WHHL females. Superovulation of females reliably produced expanded litters of WHHL rabbits. Plasma lipids were measured in expanded litters of Japanese White WHHL (JW-WW) and English Half-lop WHHL (EHL-WW) rabbits. The variance of plasma cholesterol within sibships was two- to three-fold less than that between-litters. Intraclass correlation of total cholesterol within litters of EHL-WW was 0.72 and within litters of JW-WW was 0.67. These data provide evidence of genetic modulation of hypercholesterolemia in WHHL rabbits and demonstrate that experimental designs in which littermates are paired across groups can decrease the number of animals needed or increase the sensitivity of hypothesis tests by two- to threefold.     

Effect of propofol on oxidative stress status in erythrocytes from dogs under general anaesthesia

Background

Piglets are born with eight sharp teeth that during nursing can cause facial lesions on littermates and teat lesions on the sow. Teeth grinding in piglets is therefore often practiced to reduce these lesions. The aim of this study was to assess the consequences of grinding piglet teeth in regard to the occurrence of lesions. In this study the piglets' teeth were grinded in 28 litters, and in 36 litters the piglets' teeth were kept intact. Twice, one time during the first week and one time during the second week after birth facial lesions of the piglets were scored and the teats of the sows were examined for lesions. The facial lesion score accounted for the amount and severity of lesions. The individual observations on piglets in the litter were synthesized in a litter facial lesion score.

Findings

69.8% and 43.5% of the piglets had facial lesions in week 1 and week 2 respectively. The effect of treatment was not significant on litter facial lesion score. The litter facial lesion score was higher in week 1 than in week 2 (p < 0.001) and higher in large litters (p = 0.003) than in small litters. Mortality between week 1 and week 2 was higher in litters with intact teeth (p = 0.02). Sow teat lesions only occurred if litters had intact teeth.

Conclusions

According to our results teeth grinding is only justifiable in large litters.     

Litter sex ratios in Richardson’s ground squirrels: long-term data support random sex allocation and homeostasis

When costs of producing male versus female offspring differ, parents may vary allocation of resources between sons and daughters. We tested leading sex-allocation theories using an information-theoretic approach and Bayesian hierarchical models to analyse litter sex ratios (proportion males) at weaning for 1,049 litters over 24 years from a population of Richardson’s ground squirrels (Urocitellus richardsonii), a polygynandrous, annually reproducing mammal in which litter size averages from six to seven offspring and sons are significantly heavier than daughters at birth and weaning. The model representing random Mendelian sex-chromosome assortment fit the data best; a homeostatic model received similar support but other models performed poorly. Embryo resorption was rare, and 5 years of litter data in a second population revealed no differences in litter size or litter sex ratio between birth and weaning, suggesting that litter size and sex ratio are determined in early pregnancy. Sex ratio did not vary with litter size at weaning in any of 29 years, and the observed distribution of sex ratios did not differ significantly from the binomial distribution for any litter size. For 1,580 weaned litters in the two populations, average sex ratio deviated from parity in only 3 of 29 years. Heavier females made a greater reproductive investment than lighter females, weaning larger and heavier litters composed of smaller sons and daughters, but litter sex ratio was positively related to maternal mass in only 2 of 29 years. Such occasional significant patterns emphasize the importance of multi-season studies in distinguishing infrequent events from normal patterns.     

Relationship between beta-adrenoceptors and coronary blood flow heterogeneity

The purpose of this study was to investigate the hypothesis that the heterogeneous distribution of beta adrenoceptors contributes to the control of flow heterogeneity in the canine myocardium. beta adrenoceptor density and affinity were measured simultaneously with coronary blood flow in multiple sections of the left ventricle of 14 anesthetized open chest dogs. Radioactive microspheres were used for the measurement of blood flow. The left ventricle was cut into 15 subepicardial (EPI) and 15 subendocardial (ENDO) sections. Receptor density (Bmax) and dissociation constant (Kd) were measured using [125I]-iodopindolol. The average control myocardial blood flow (MBF) was 86 +/- 15 ml/min/100 g. Isoproterenol (0.5 micrograms/kg/min) increased MBF by 82%, whereas propranolol (2 mg/kg) reduced MBF by 13%. The mean value for Bmax was unaltered by either treatment. Under control conditions, a significant positive correlation (r = 0.26, p less than 0.0001) was observed between Bmax and blood flow. In the isoproterenol treatment group, this correlation was enhanced (r = 0.49, p less than 0.0001). Beta adrenoceptor blockade led to a negative correlation. Kd showed no overall correlation with blood flow. Kd but not Bmax was significantly higher in the EPI than in the ENDO and in the base compared to the apex. There appears to be a direct linear relationship between the distribution of beta adrenoceptors and MBF distribution which is enhanced under conditions of high beta adrenergic activity. There is a correlation between beta adrenoceptor activity and blood flow distribution in the canine myocardium.