Induction of Intramembranous Particle Clusters in Mice with Nephrogenic Diabetes Insipidus
| Title: | Induction of Intramembranous Particle Clusters in Mice with Nephrogenic Diabetes Insipidus |
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| Authors: | Coffey, Aline K.; O'Sullivan, Daniel J.; Homma, Sumiko; Dousa, Thomas P.; Valtin, Heinz |
| Publisher: | American Journal of Physiology |
| Date Published: | October 01, 1991 |
| Reference Number: | 314 |
In mice with hereditary nephrogenic diabetes insipidus (NDI), the inability of vasopressin to increase hydraulic water permeability is reflected in a lack of intramembranous particle (IMP) clusters in apical membranes of inner medullary collecting ducts. The lack arises from anomalously high activity of one or two isozymes of adenosine 3',5'-cyclic monophosphate-phosphodiesterase (cAMP-PDE). We asked whether inhibition of these isozymes with rolipram and cilostamide would raise not only the tissue content of cAMP but also and simultaneously restore IMP clusters. Inner medullary collecting ducts from NDI mice were incubated in vitro. Tissue content of cAMP (fmol of cAMP per bundle) and number of IMP clusters (per 100 microns 2 of principal cell apical membrane) were, respectively: control, 44.8 +/- 13.0 and 4.16 +/- 1.49; arginine vasopressin (AVP), 31.7 +/- 8.0 and 3.98 +/- 1.56; rolipram and cilostamide, 109.7 +/- 21.0 and 58.09 +/- 15.74; and AVP plus rolipram and cilostamide, 305.7 +/- 75 and 48.63 +/- 11.03 (with the last four values showing significant difference from control and AVP only, respectively). In addition, treating NDI mice with rolipram and cilostamide in vivo reduced their high fluid turnover. We conclude that failure by AVP to increase cAMP in cells of collecting ducts, which results from anomalously high activity of one or two specific isozymes of cAMP-PDE, is the major or sole cause for the excretion of hypotonic urine in NDI mice (DI +/+ Severe strain).
This translation by the NDI Foundation is to assist the lay reader. To provide a clear, accessible interpretation of the original article, we eliminated or simplified some technical detail and complicated scientific language. We concentrated our translation on those aspects of the article dealing directly with NDI. The NDI Foundation thanks the researchers for their work toward understanding and more effectively treating this disorder.
© Copyright NDI Foundation 2007 (JC)
The authors reasoned that if they inhibited these cAMP-PDE enzymes (PDE-IV and PDE-III) with the selective inhibitors rolipram and cilostamide, it might restore the cAMP levels in the NDI mice to levels found in normal mice. And this, in turn, might allow the normal amounts of IMP clusters to be inserted in the collecting duct cell membranes. If this were so, it could alleviate or eliminate the mice's polyuria (chronic passage of large volumes of urine) and polydipsia (chronic, excessive thirst), the two primary symptoms of NDI.
The authors' experiments had two levels, one utilizing NDI kidney tissue in laboratory cultures, and one using live NDI mice. The authors took samples of NDI mice kidney tissue and measured three things: 1. tissue content of cAMP, 2. number of IMP clusters, 3. proportion of total membrane area occupied by IMP clusters. The authors created four groups: 1. the control tissue, 2. tissue with arginine vasopressin (AVP) added to it (AVP, when it binds with the vasopressin-2 receptor, initiates the molecular sequence which inserts IMPs into the collecting duct cell membranes.) 3. tissue with rolipram and cilostamide added, and 4. tissue with rolipram, cilostamide and AVP added.
The authors found no difference between the control tissue and tissue with just AVP added (group two). However, they did find significantly more cAMP, IMP clusters, and higher proportions of membrane area occupied by IMP clusters in tissue cultures three and four. The only difference between these last two tissue cultures was that tissue culture four had a higher cellular content of cAMP. Otherwise these two tissue cultures had similar increases in the other variables.
These results indicated that using rolipram and cilostamide inhibited cAMP-PDE-IV and cAMP-PDE-III in mice, allowing them to complete the molecular sequence which inserts IMPs in their proper place. The authors thought administering rolipram and cilostamide to live NDI mice should allow the mice to concentrate urine and reabsorb water normally.
To prove this, the authors injected one group of NDI mice with rolipram and cilostamide and measured their urine output against a control group of normal mice. During this period, the urinary flow and water intake of the NDI mice fell significantly, and their urine osmolality (a measure of the concentration of a particular type of particles in the urine) significantly increased. When treatment stopped, these variables went back to their NDI values.
The authors concluded that the major or sole defect in this NDI mice strain was the increased activity of cAMP-PDE-IV and, possibly, cAMP-PDE-III. This abnormal activity level can be inhibited, and this will relieve the symptoms of NDI in this strain of mice as long as the treatment continues.