[Fetal human myocardium. Proliferation of the myocytes and development of the cardiac interstitium in the last two gestational trimesters]

PURPOSE

To determine prenatal myocardial quantitative changes by using stereology.

METHODS

Twenty-six human fetuses were studied (16 in the 2nd trimester and 10 in the 3rd trimester). The hearts were dissected, weighted, fixed in the Bouin's solution for 12 h, embedded in paraplast, sectioned and stained by HE and trichrome of Gomori. Ten random microscopic fields were analyzed by heart. The following parameters were studied: Vv[myocyte] and Vv[interstitium] (%) (the volume densities of the cardiac myocyte and interstitium), and Nv[myocyte] (1/mm3) (the numerical density of the cardiac myocytes) by the dissector method. The total number of myocytes (N[myocyte]) and the mean volume of the myocytes (V[myocyte]) were also determined. The differences were tested by the Mann-Whitney non-parametric test.

RESULTS

The cardiac weight increased of 1.95 to 9.1 g, the Vv[myocyte] decreased from 85.18 to 77.78% and the Vv[interstitium] increased from 14.83 to 22.22%. The Nv[myocyte] decreased from 68.86 x 10(4) to 57.40 x 10(4)/mm3. The V[myocyte] increased from 1214.38 to 1412.31 microns3 and the N[myocyte] increased from 1.36 x 10(9) to 5.06 x 10(9) myocytes. These differences were statistically significant (p < 0.05).

CONCLUSION

These results suggest the development of the myocardium at the end of the fetal human period as being mainly hypertrophic to the myocyte and the cardiac interstitium.

Quantitative study of the myocardium in human embryos

We studied six human embryos of the second gestational month (postsomitic period, from stages 15 to 23). They were fixed in 4% formaldehyde and serially sectioned. Stereological determinations were made from the compact layer of the ventricular myocardium: a) volume density of the myocardial parts: myocytes (Vv[myocyte]) and interstitium (Vv[interstitium]), b) numerical density of the myocytes (Nv[myocyte] mm3) calculated from six optical disector pairs per embryo, c) total number of myocytes (N[myocyte]), d) volume of the myocytes (V[myocyte] micron 3). In embryos from stages 15 to 19 the quantities of the myocytes and interstitium remained practically unchanged (no statistical difference was found). However, the volume of the ventricular myocardium mass increased more than 5 times during this period. Comparing embryos of stages 15 and 23, the mean value of the Nv[myocyte] decreased about 30 per cent, while N[myocyte] increased almost 2,000 per cent in the same period. Simultaneously, the volume of the ventricular myocardial mass increased almost 30 times, and Vv[myocyte] and Vv[interstitium] showed a small increase in the myocyte component (about 20 per cent), with a decrease of the interstitial component (about 70 per cent). In the early post-somitic period the human myocardium has a relatively small number of small myocytes, in the late post-somitic period it is composed of large and relatively abundant cardiac myocytes. The conspicuous increase in the ventricular myocardial volume observed in stage 23 seems not to be related to the increase in the interstitial portion of the myocardium. These arguments suggest both the enlargement and the division of the cardiac myocytes during the post-somitic period.

Current advances on the study of snail-snail interactions, with special emphasis on competition process

Field work research on population dynamic of snails from the regions of Belo Horizonte and Lagoa Santa give much information about interactions among two or more species of mollusks: Pomacea haustrum, Biomphalaria glabrata, B. tenagophila, B. straminea and Melanoides tuberculata. Data ranging from two years to several decades ago suggest that the Pampulha reservoir is like a cemetery of B. glabrata and B. straminea, species that coexist for more than 14 years in a small part of a stream, whereas only B. glabrata lives in all the streams of the basin. In the last ten to twenty years B. tenagophila has coexisted with P. haustrum and M. tuberculata in the Serra Verde ponds and in the Pampulha dam. However these species have not settled in any of the brooks, except temporarily. The data suggest that the kind of biotope and the habitat conditions are decisive factors for the permanence of each species in its preferencial biotope. B. glabrata, natural from streams and riverheads, quickly disappears from the reservoirs and ponds where it coexists with other species for a short time, independently of the competitive process. Competition needs to be better studied, since in Central America and Caribean islands this kind of study has favored the biological control of planorbid species.

[Competitive behavior of Biomphalaria glabrata and Biomphalaria tenagophila--laboratory studies]

Observation about cohabitation among B. glabrata and B. tenagophila revealed a greater vulnerability of B. tenagophila population during the process of competition when its density was severely decreased in 12 trials, moderate in 2 trials. It was higher than B. glabrata in only one trial. Some snail water chemical parameters analysed such as pH, alkalinity, conductivity and oxygen dissolved, and the viability rate of batch of eggs didn't give subsidy to explain the competition mechanism. The newly-born survival, in the situation of cohabitation, was low for both species. This reveals the existence of intra and interspecific competitive interaction. The fertility rate reduction of B. tenagophila during the cohabitation was considered as a cause of its exclusion. One of the factors that seems to have influenced the fertility rate was a possible wrong crossing.

Preference of Biomphalaria tenagophila among macrophytes and their periphytons determined through the degree of attractiveness

In presence of extracts of six flowering plants the Biomphalaria tenagophila was more attracted to four them in the following sequence: Nasturtium pumilum > Polygonum acre > Commelina sp. = Echinochloa crusgalli. The periphyton of these flowering plants attracted in the same way the B. tenagophila but without no preference for either of them. Reporting the results that behavior may be evaluated as a co-evolution between snail and plants.

[Susceptibility of Biomphalaria tenagophila hybrids to the LE (BH) strain of Schistosoma mansoni]

"Híbridos" de Biomphalaria tenagophila provenientes dos cruzamentos de linhagens albinas de Belo Horizonte (BH) ou de Joinvile (SC), com melânicos de Cabo Frio (CF), do Taim (Ta) ou de Curitiba (PR), submetidos à infecção pela cepa do Schistosoma mansoni de Belo Horizonte (=LE), apresentaram os seguintes resultados: em F1, os "híbridos" TaSC, PRSC e CFTa exibiram taxas de 4,5%, 12,5% e 11,2% de suscetibilidade; em F2, todos os "híbridos" foram negativos e em F3, um exemplar albino, filho de (CFBH) ². TaBH se infectou com a LE. Dentre os controles, a B. glabrata apresentou taxas de 66,7 a 93,6% de suscetibilidade à LE e a B. tenagophila de Joinvile exibiu taxas de infecção de 17,1 e 33,3% pela cepa SJ; e os "híbridos" BHTa e BHCF, taxas de 6,0 a 53,8% também pela cepa SJ. Houve grande influência da linhagem materna nas taxas de suscetibilidade. Devido ao fato de descendentes do cruzamento de linhagens refratárias a LE (CF, Ta e BH), terem se infectado, é recomendado o uso de "híbridos" para a detecção de gens de suscetibilidade em tais linhagens. São ainda discutidas, a necessidade do uso de maior número de miracídios nos testes de infecção e a falta de relação entre a freqüência de contatos parasitas-hospedeiros e as taxas de infectividade. Considerando que estas dependem de características genéticas preexistentes na população, a cepa LE seria uma variedade genética (ou raça) distinta da cepa SJ, dotada de pouca aptidão em infectar as diversas populações de B. tenagophila, exceto a de Joinvile (SC).