|
|
||||||||
Eur J Cardiothorac Surg 2005;28:811-815
© 2005 Elsevier Science NL
a Department of Cardiothoracic Surgery, Southampton General Hospital, UK
b Centre for Developmental Origins of Health and Disease, University of Southampton, Princess Anne Hospital, Southampton SO16 5YA, UK
c Department of Veterinary Reproduction, Royal Veterinary College, University of London, UK
d Division of Reproductive Health, Endocrinology and Development, Guy's King's St Thomas Hospital, London, UK
Received 23 February 2005; received in revised form 18 August 2005; accepted 31 August 2005.
* Corresponding author. Tel.: +44 115 9691169; fax +44 115 8402605. (Email: m.hanson{at}soton.ac.uk).
| Abstract |
|---|
|
|
|---|
Key Words: Coronary artery bypass conduits Vascular tone and reactivity
| 1. Introduction |
|---|
|
|
|---|
| 2. Methods |
|---|
|
|
|---|
Welsh mountain ewes of uniform age, weight and body condition were bought from a known supplier (Royal Veterinary College, University of London). Upon enrolment into the study, the ewes were assigned to three dietary groups. The oestrous cycles of the sheep were synchronised using vaginally inserted progesterone-impregnated sponges (Chronogest, Intervet), which were removed 48 h prior to tupping. Rams of the same breed were introduced on Day 1 of the study (Day 0 was assumed to be conception). On Day 16, intravenous blood samples were extracted from the ewes and an ELISA progesterone assay was performed. Animals with low progesterone were deemed not pregnant and removed from the study. On Day 60 of gestation, each ewe was scanned to confirm pregnancy and any animal not pregnant was withdrawn from the study.
2.2 Dietary manipulation
The animals were individually-housed indoors prior to conception for approximately one week and fed a complete diet ration according to body weight. This diet consisted of barley, wheat, micronised full fat soya, grass meal, molasses, chopped straw, calcium carbonate, dicalcium phosphate salt and sheep vitamin/mineral supplement, which provided 10.8 MJ/kg metabolisable energy, 14.98 g/kg crude protein and contained 88.4% dry matter. Feed was allocated based on the advisory manual prepared by the AFRC Technical Committee on responses to nutrients.
The ewes were then randomly assigned to one of three dietary groups. The nutritional challenges of the groups are summarised in Fig. 1 .
|
Ewes in the pre-natal restricted group (UC) were fed a complete diet ad libitum until Study Day 0. The animals were then fed 50% of their energy requirement based on body weight until Study Day +31. These animals were then fed 100% of their nutritional requirements throughout the remainder of gestation. Their male offspring (n = 6) were then fed a pelleted diet with hay following weaning at 12 weeks.
Ewes in Group UU underwent an identical pre-natal restriction as those in Group UC. In addition, following weaning, their offspring underwent a further nutrient restriction. This restriction was individually calculated in order to reduce the body weight to 85% of the predicted growth for each lamb based on its 012-week growth trajectory. This restricted diet was given between 12 and 25 weeks following birth, after which the male offspring (n = 7) were transferred back onto a pelleted diet with hay.
2.3 Determination of isolated artery function
At 130 weeks of age, the male offspring of the ewes were euthanised using an overdose of pentobarbitone sodium (0.8 ml/kg i.v., 200 mg/ml, Animalcare Ltd., York, UK). Immediately following death, the left internal thoracic was harvested from the 2nd intercostal space to its bifurcation by an investigator who was blinded as to the dietary group of the sheep. Following harvesting, the artery was excised and immersed in ice-cold physiological salt solution (PSS) (consisting of (mM): NaCl, 119; KCl, 4.7; CaCl2, 2.5; MgSO4, 1.17; NaHCO3, 25; KH2PO4, 1.18; EDTA, 0.026; and D-glucose, 5.5) in order to reduce the risk of ischaemic damage to the arteries. The arteries were dissected free of connective tissue and the distal centimeter excised and then divided into four segments as ring preparations. Ring segments were then mounted on a small vessel wire myograph (Multi Myograph Model 610M; J.P. Trading, Aarhus, Denmark). The arterial ring segments were bathed in physiological salt solution at 37 °C gassed with a mixture of 95% O2 and 5% CO2 (pH 7.4). After an equilibration period of 30 min, PSS was exchanged with fresh, pre-warmed and pre-oxygenated Ca-free PSS. The rings were then stretched in progressive steps and the tension recorded. The optimal point on their lengthtension relationship was then determined by calculating the internal vessel circumference equivalent to a transmural pressure of 100 mmHg (using the Laplace relationship) and setting the arterial diameter equal to 0.9 x IC100 as per previously validated techniques [9].
2.4 Experimental protocol
Following optimisation of the diameter of the rings as described above, all preparations were subsequently challenged with KPSS (125 mM K, equimolar substitution of NaCl with KCl in PSS) for 5 min, to obtain a reference contraction. The rings were then washed out, and a standardised protocol was followed in order to assess the contraction and relaxation properties of the internal thoracic artery of each animal.
Contraction data were generated by measuring cumulative doseresponses to PE (108 to 103 M) and to endothelin (1013 to 107 M). Relaxation was assessed by pre-constricting the ring segments with 107 M endothelin and measuring the relaxation to adenosine (1011 to 104 M) and bradykinin (1012 to 105 M). At the end of the experiment, papaverine (101 M) was added to the organ bath in order to record the absolute resting passive tension. All drugs and chemicals except endothelin (Bachem, St Helens, UK) were obtained from Sigma Chemical Co. (Poole, UK).
2.5 Data analysis
Basal tone and contraction responses to agonists were calculated as percentage of maximum 125 mM KPSS-induced contraction and expressed as mean ± SEM. The spontaneous or resting basal tone was calculated by comparing the tension prior to KPSS contraction with the absolute resting passive tension using a standardised technique and expressed as a percentage of the amplitude of the reference contraction ± SEM [10]. Relaxant responses to agonists were calculated as percentage relaxation of the endothelin-induced contraction and expressed as mean ± SEM.
Concentrationresponse curves to agonists were fitted to a sigmoidal curve with a four-parameter logistic equation using non-linear regression (Prism 3.0; GraphPad Software Inc, San Diego, CA, USA). It should be noted that all agonists did produce curves which could be fitted to a sigmoidal curve.
Maximum responses and pEC50 values were obtained from the fitted data, where the EC50 was the concentration (molar) of the agonist that produced 50% of its maximum response. Statistical analyses were performed using one-way ANOVA and a Bonferroni post hoc test to compare the different groups. Significance was assumed if p < 0.05.
| 3. Results |
|---|
|
|
|---|
|
|
Animals in Group UC showed statistically significant increase in sensitivity to phenylephrine (PE) as compared with Group CC (log EC50: 6.23 ± 0.04 M vs 5.74 ± 0.17 M, p = 0.036), as shown in Table 2. The overall maximal response to PE was, however, similar in all three groups, and there was no significant difference in the PE doseresponse between Groups CC and UU, as illustrated in Fig. 2 .
|
3.4 Relaxant responses
Endothelin pre-contraction was similar in all three groups (results not shown). Bradykinin and adenosine produced sigmoidal concentration-dependent relaxation of endothelin pre-contracted arteries but there were no differences in the maximal response or EC50 values between the groups (Table 3
).
|
| 4. Discussion |
|---|
|
|
|---|
Although this study did show that pre-natal undernutrition was associated with vascular dysfunction, it should be noted that there were no differences in birth weight between the three groups. This finding correlates with previous studies [20] in illustrating that following undernutrition in utero, reduction in birth weight is not a necessary pre-requisite for perturbed cardiovascular function in adulthood. Similarly at post-mortem, we found no differences in body weight, crownrump length, BMI or ponderal index between the three groups. Although the effect of foetal undernutrition on adult growth parameters is beyond the scope of this report, these findings do suggest that birth weight and biometric measures of post-natal growth are relatively poor proxies for foetal nutrition.
The new major finding in this study is the observation that the effects of a pre-natal nutritional challenge are attenuated by continuing this restriction after birth. The issue of interactions between the pre- and early post-natal environment has recently been discussed by Gluckman and Hanson [21] in terms of a so-called predictive-adaptive response. In their model, the foetus constantly interprets the environment created by the maternal milieu and placental function and uses this information to predict the likely post-natal environment. For example, if the foetus has a poor nutritional diet in utero, it will then predict a nutritionally poor post-natal environment and then chooses a developmental path which will optimise its survival in such an environment. If however, the post-natal environment fails to confirm with these expectations, then the offspring will have made inappropriate metabolic adaptations, which instead of aiding its survival, may lead to disease in adulthood. Our findings do appear to support this hypothesis by demonstrating that mismatches between foetal and post-natal environment are the strongest determinants of vascular dysfunction. What remain unclear are the cellular mechanisms underlying these vascular changes. One possibility may lie in epigenetic changesit is possible that changes in the post-natal environment may lead to changes in DNA methylation [21], which may in turn lead to alterations in the gene expression of vasoactive substances such as vascular endothelial growth factor [22]. Whilst highly speculative, this explanation does at least illustrate a potential mechanism for linking perinatal nutritional with vascular function.
The findings in this study raise the obvious question as to the relevance of this work in humans. Although it would be preferable to directly analyse the effect of pre-natal factors on human ITA function in humans, a prospective study on vascular function would clearly be ethically inconceivable. Our rationale for using sheep in this study is the fact that they share a number of developmental features with humans; and unlike rodents they typically produce singleton offspring. In addition, the sheep ITA been extensively utilised as a model for studying graft function following coronary artery bypass surgery [23,24]. In view of this, we believe it is reasonable to consider extrapolating the findings of our study to humans. If so, this in turn raises questions of the potential clinical importance of these findings. Although our animals were studied at the age of only 130 weeks (which in human terms equates to a post-adolescent male), evidence from epidemiological studies suggests that the vascular dysfunction seen as a consequence of foetal undernutrition persists into old age [25]. Given this finding, and the fact that many of the inotropic drugs used in the peri-operative period following cardiac surgery have alpha and beta-mimetic activity, alterations in the vascular reactivity of the type seen in this study may indeed have important clinical consequences in patients undergoing coronary artery bypass surgery.
In summary, we have shown that foetal and early post-natal undernutrition leads to altered internal thoracic artery vasoreactivity in sheep. These findings suggest that undernutrition in foetal and early life may be an important determinant of graft function in later life.
| Acknowledgments |
|---|
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
C. Torrens, T. H. Snelling, R. Chau, M. Shanmuganathan, J. K. Cleal, K. R. Poore, D. E. Noakes, L. Poston, M. A. Hanson, and L. R. Green Effects of pre- and periconceptional undernutrition on arterial function in adult female sheep are vascular bed dependent Exp Physiol, September 1, 2009; 94(9): 1024 - 1033. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. K. Cleal, K. R. Poore, J. P. Boullin, O. Khan, R. Chau, O. Hambidge, C. Torrens, J. P. Newman, L. Poston, D. E. Noakes, et al. Mismatched pre- and postnatal nutrition leads to cardiovascular dysfunction and altered renal function in adulthood PNAS, May 29, 2007; 104(22): 9529 - 9533. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN | EUR J CARDIOTHORAC SURG |
| J THORAC CARDIOVASC SURG | ICVTS | ALL CTSNet JOURNALS |