CARDIOVASCULAR JOURNAL OF AFRICA • Vol 22, No 1, January/February 2011
AFRICA
17
rats with an increased tachycardic reflex may be more susceptible
to higher sympathetic nervous activity, since we did not measure
this. Future studies are necessary to explore this possibility.
The currently reported differences in baroreflex sensitivity
between SHRs from the same laboratory might be due to factors
such as spontaneous mutations, genetic contamination of the
breeding stock, or non-genetic influences (e.g. vertically trans-
mitted diseases or differences in the prenatal and neonatal envi-
ronments existing at different breeding facilities).
17
In the article
that describes the initial development of the SHR, Okamoto and
Aoki
18
stated that the rats were selected from a Wistar strain that
had been maintained by inbreeding. Therefore, it is conceivable
that the normotensive Wistar rats sent from Kyoto to the National
Institute of Health (NIH) in 1971 were at least partially inbred.
However, the precise circumstances of the brother–sister mating
are not clear because records from the NIH indicate that: (1) the
SHR were developed from an ‘outbred Wistar Kyoto male’ and
(2) the Wistar rats from Kyoto used by the NIH to breed WKY
were from ‘non-inbred’ stock.
18
In this study baroreflex function was evaluated in conscious
rats, since baroreflex activity is blunted under anesthesia,
19,20
thus
reducing the range of HR, which would impact on the outcome
in an analysis on a restricted portion of the baroreflex response.
Therefore, we believe that this study provides accurate informa-
tion regarding the discrepancy of baroreflex function between
rats of the same strain (in our case the SHR strain). It would also
be interesting to compare other cardiovascular reflexes (such as
the cardiopulmonary reflex and chemoreflex) in other strains of
rat, such as the SHR stroke prone (SHRSP), and in other animals,
such as rabbits and mice.
These data present clinically relevant information, since
the baroreceptor reflex is currently studied mainly in different
models and strains of rats, aiming to prevent hypertension devel-
opment in the human,
11,20,21
due the fact that reduced baroreflex
function is indicative of cardiovascular disease.
22-24
Since SHR
strains are being used extensively throughout the world, research-
ers should be aware of the genealogical background of the SHR.
It was also previously shown that genetic markers of WKY,
such as asylosterase isozyme patterns, differed among the avail-
able strains of WKY (unpublished observation). Such informa-
tion is useful for researchers who are using SHRs in comparison
with WKY, and may assist in understanding the correct usage of
SHRs, as well as the control WKY strain.
Conclusion
We demonstrated a significant variation in the baroreflex sensi-
tivity between SHRs of the same laboratory and we concluded
that this may significantly influence future studies employing the
SHR as research model.
This research was supported by public funding from Fundação de Amparo à
Pesquisa do Estado de São Paulo (FAPESP).
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