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G R Snow

Publications and source records attributed to G R Snow.

13 recordsLinked to original sources
PubMed1987

Effects of continuous 17 beta-estradiol administration on the periosteal and corticoendosteal envelope activity in spayed beagles.

Histomorphometric analyses of resorptive and formative parameters of the periosteal and corticoendosteal bone envelopes were performed on ribs from intact, spayed and spayed 17 beta-estradiol-supplemented Beagle dams. Dynamic formative features were evaluated after 2 pulses of in vivo tetracycline administration. The results indicated that following oophorectomy there was an increase in resorptive surfaces on the periosteum and corticoendosteum, and a decline in formative activity on these same envelopes. With continuous 17 beta-estradiol supplementation, the resorptive surfaces on both the periosteum and corticoendosteum of the spayed dams decreased. The formative activity on the periosteum seemed to decline further after the administration of 17 beta-estradiol, while on the corticoendosteum it tended to be restored to the level obtained for the intact dams. The increase in mineralization lag-time detected on the periosteum following oophorectomy appears not to be corrected by continuous 17 beta-estradiol supplementation in the spayed dams.

Animals↗
PubMed1986

The effects of 17 beta-estradiol and progestagen on trabecular bone remodeling in oophorectomized dogs.

We present the results of the static and dynamic histomorphometric analyses of parameter measurements of trabecular bone remodeling activity in nonoophorectomized, untreated oophorectomized, 17 beta-estradiol-supplemented oophorectomized, as well as progestagen-supplemented oophorectomized beagle dams. If the spayed beagle dam can be considered a model in which one may equivalate bone changes occurring in the ovarian hormone-deficient human female, we reach the following conclusions: The presence or absence of quasi-physiological levels of single ovarian hormones do affect the status of trabecular bone. The evidence indicates that the presence or absence of individual ovarian hormones do not have a simple effect on trabecular bone remodeling. Apart from affecting the numbers of new bone remodeling units (BMUs) that are initiated in unit time, their effect is seen to be extended to the working efficiency of existing osteoclasts and osteoblasts. The effect is also manifest on the total amount of work performed by the collections of osteoclasts and osteoblasts that provide the respective resorptive and formation phases of the BMU. Finally, we are led to believe that there may be a close interdependence both in physiological activity and therapeutic response between the four active bone envelopes. Such protein effects have hitherto not received their due consideration from researchers in this field.

Animals↗
PubMed1986

Short-term chronic fluoride administration and trabecular bone remodeling in beagles: a pilot study.

We carried out a pilot project to examine the alterations in trabecular bone remodeling activity of spayed Beagle dams exposed to 0.7 mg/kg body wt/day of sodium fluoride (NaF) for a 6 month period. The results indicated that short-term NaF administration does activate trabecular bone remodeling activity by stimulating the formation of new Basic Multicellular Units (BMUs) of bone remodeling activity. However, interference with bone cell differentiation, with the functional efficiency and/or life-span of individual osteoclasts and osteoblasts followed. Cellular toxic effects appear early with NaF administration, and as such, suggest that the increases in bone mass seen early in the course of NaF treatment may be negated by prolonged administration of this substance. However, preservation of bone mass will probably result with long-term therapy, due to decreases in numbers of bone cells, in their functional efficiencies, and in their individual life-spans.

Animals↗
PubMed1986

Surface activity on the periosteal and corticoendosteal envelopes following continuous progestogen supplementation in spayed beagles.

Resorptive and formative characteristics on the periosteal and corticoendosteal bone envelopes were assessed on the ribs of intact, spayed and medroxyprogesterone acetate (MPA)-supplemented Beagle dams. Histomorphometric analyses of the alterations on surface activities of these two envelopes were carried out using tetracycline labeling. It was found that continuous administration of progestogen decreased the extent of resorptive surfaces on the corticoendosteal surfaces of progestogen-treated animals vs. spayed animals. On the periosteal surfaces the progestogen-treated dogs showed a marked increase in formation when compared to spayed and intact dogs. As a result of continuous progestogen treatment, mineralization lag time was shortened on the corticoendosteum and periosteum of progestogen-treated animals when compared to the same surfaces on the bones of intact and spayed animals.

Animals↗
PubMed1986

Bone remodeling in the lumbar vertebrae of young adult beagles.

Thirty-two static and dynamic histomorphometric determinants of tetracycline-labeled trabecular bone were determined for the L1 and L3 vertebrae of 5 intact and 6 oophorectomized Beagle bitches. Because significant differences in trabecular bone remodeling between the 2 vertebrae were not found, we concluded that the mean of the combined L1 and L3 data, or the mean of data generated from individual vertebrae, may be representative of trabecular bone remodeling of the lumbar vertebrae of Beagles.

Animals↗
PubMed1985

The effects of continuous estradiol therapy on cortical bone remodeling activity in the spayed beagle.

Ribs from 6 oophorectomized and 4 17 beta-estradiol-supplemented spayed, 4-year-old Beagle dams were subjected to histomorphometric analyses to determine what effects continuous estradiol treatment of 9 months duration had on the Basic Multicellular Unit (BMU) of cortical bone remodeling. The findings of this study suggest that 17 beta-estradiol has a two-step mode of action. First, this estrogen directly suppresses the formation of new BMUs. Secondly, it causes uncoupling of the Resorption/Formation (R/F) mechanism within each BMU, together with the creation of an approximate 1:1 balance between bone resorption and bone formation. This balance is probably responsible for the preservation of cortical bone mass seen to occur with continuous estrogen replacement therapy.

Animals↗
PubMed1985

The effects of continuous progestogen treatment on cortical bone remodeling activity in beagles.

Cortical bone remodeling measurements were carried out on the ribs of 6 spayed and 5 progestogen-treated spayed Beagle dams which had been subjected to a period of observation equal to more than 1 sigma of intact canine bone remodeling activity. Analyses of static and dynamic features indicated that continuous medroxyprogesterone acetate replacement therapy altered the rates of cortical bone remodeling activity. In the progestogen-treated dams, more Basic Multicellular Units (BMUs) were activated, exhibiting shortened resorption and formation times. Thus, this progestogen appears to play a significant role in regulating cortical bone cell activity and, as such, suggests that progesterone may play a part in the prevention or slowing down of cortical bone loss in females following menopause or oophorectomy.

Animals↗
PubMed1985

Differences in periosteal and corticoendosteal bone envelope activities in spayed and intact beagles: a histomorphometric study.

Resorptive and formative characteristics of the periosteal and corticoendosteal envelopes of the ribs of intact and spayed Beagle dams were studied. Six 4-year-old Beagle dams were spayed at source and kept under observation for 12 months. Four intact age- and weight-matched Beagle dams were used as controls. Before euthanizing, all dams received tetracycline labeling of their bones. Histomorphometric analyses of resorptive and formative parameters of the periosteal and corticoendosteal envelopes were carried out blind. The results indicated that following oophorectomy, there is an increase in resorptive surfaces on the periosteum and corticoendosteum, and a decline of formative activity on these same envelopes. These changes were manifested to a greater extent on the corticoendosteum. The lack of ovarian hormones contributes to an increase in the mineralization lag-time on the periosteum. Although in both control and spayed dams a similar pattern of surface activity was observed on both envelopes investigated, the differences in degree may be attributable to the ovarian hormone withdrawal.

Animals↗
PubMed1984

Oophorectomy and cortical bone remodeling in the beagle.

Cortical bone remodeling measurements were carried out on the ribs of 6 spayed and five control Beagle dams which had been subjected to a period of observation equal to more than one sigma of cortical bone remodeling activity. The results of the measurements of static and dynamic parameters indicate that the lack of ovarian hormones does not produce a major alteration in the rates of cortical bone remodeling, but does result in an increase in the number of resorption spaces per mm2 of cortical bone without altering the parameters of bone function. This latter fact supports the hypothesis that decreased levels of circulatory ovarian hormones may influence the duration of the resorption activity as well as possibly uncoupling the resorption/formation (R/F) mechanism of the bone remodeling unit.

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